Tslib unused
along with one repeated string and a case in `_Timedelta.__richcmp__` that is not reachable.

- [ ] closes #17379
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17402?src=pr&el=h1) Report
> Merging [#17402](https://codecov.io/gh/pandas-dev/pandas/pull/17402?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/062f6f118fe4ea439ae255a8ff886a532e20ecdb?src=pr&el=desc) will **decrease** coverage by `0.04%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/17402/graphs/tree.svg?src=pr&token=eZ4WkYLtcO&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/17402?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #17402      +/-   ##
==========================================
- Coverage   91.03%   90.99%   -0.05%     
==========================================
  Files         163      163              
  Lines       49580    49580              
==========================================
- Hits        45137    45116      -21     
- Misses       4443     4464      +21
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.77% <ø> (-0.03%)` | :arrow_down: |
| #single | `40.26% <ø> (-0.07%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/17402?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/17402?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/17402?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `63.23% <0%> (-1.82%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/17402?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.72% <0%> (-0.1%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17402?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/17402?src=pr&el=footer). Last update [062f6f1...3ebd4ab](https://codecov.io/gh/pandas-dev/pandas/pull/17402?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Closes #17379