DOC: removed versionadded <0.17 in doc strings
Cleaned up old references to when functionality was added.

See also #17442, #17442, #17404.
lgtm. ping  on green. It's green, I think? The failure doesn't seem to have anything to do with my pull request, right?

Is it possible to run that single test again without running the whole test suite? Alternative, should I push some irrelevant change, to see it the error happens again? @topper-123 : Just ping us regarding unrelated failures, and we'll take care of it for you. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=h1) Report
> Merging [#17504](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/83436af8ae1ccad49b7ceac7471c060d823d10ab?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/17504/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #17504      +/-   ##
==========================================
- Coverage   91.18%   91.16%   -0.02%     
==========================================
  Files         163      163              
  Lines       49543    49543              
==========================================
- Hits        45177    45168       -9     
- Misses       4366     4375       +9
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.95% <ø> (ø)` | :arrow_up: |
| #single | `40.21% <ø> (-0.07%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/sparse/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc3BhcnNlL3Nlcmllcy5weQ==) | `95.09% <ø> (ø)` | :arrow_up: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.77% <ø> (-0.1%)` | :arrow_down: |
| [pandas/core/indexes/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZXMucHk=) | `95.52% <ø> (ø)` | :arrow_up: |
| [pandas/core/reshape/reshape.py](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS9yZXNoYXBlLnB5) | `99.29% <ø> (ø)` | :arrow_up: |
| [pandas/core/indexes/category.py](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9jYXRlZ29yeS5weQ==) | `98.54% <ø> (ø)` | :arrow_up: |
| [pandas/core/strings.py](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc3RyaW5ncy5weQ==) | `98.46% <ø> (ø)` | :arrow_up: |
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `91.98% <ø> (ø)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=footer). Last update [83436af...7cb1a4a](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=h1) Report
> Merging [#17504](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/83436af8ae1ccad49b7ceac7471c060d823d10ab?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/17504/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #17504      +/-   ##
==========================================
- Coverage   91.18%   91.16%   -0.02%     
==========================================
  Files         163      163              
  Lines       49543    49543              
==========================================
- Hits        45177    45168       -9     
- Misses       4366     4375       +9
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.95% <ø> (ø)` | :arrow_up: |
| #single | `40.21% <ø> (-0.07%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/indexes/datetimes.py](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9kYXRldGltZXMucHk=) | `95.52% <ø> (ø)` | :arrow_up: |
| [pandas/core/sparse/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc3BhcnNlL3Nlcmllcy5weQ==) | `95.09% <ø> (ø)` | :arrow_up: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.77% <ø> (-0.1%)` | :arrow_down: |
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `91.98% <ø> (ø)` | :arrow_up: |
| [pandas/core/strings.py](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc3RyaW5ncy5weQ==) | `98.46% <ø> (ø)` | :arrow_up: |
| [pandas/core/reshape/reshape.py](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS9yZXNoYXBlLnB5) | `99.29% <ø> (ø)` | :arrow_up: |
| [pandas/core/indexes/category.py](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9jYXRlZ29yeS5weQ==) | `98.54% <ø> (ø)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=footer). Last update [83436af...7cb1a4a](https://codecov.io/gh/pandas-dev/pandas/pull/17504?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @topper-123 @jreback : Everything is green and good to go now. thanks!