CLN: _try_coerce_result, redundant dtypes.missing method
Started this branch with the idea of making DatetimeBlock, TimedeltaBlock, DatetimeTZBlock define _try_coerce_result using self._holder._from_sequence (which I still think is worthwhile, cc @TomAugspurger ) and got side-tracked.  This ends up just being some cleanup and removal of a redundant method.

Tiny perf bump expected from optimizing NaT checks in _libs.missing.  Further improvements/cleanups may be possible pending #24607.

The object-dtype cases in try_coerce_result are no longer hit following #24606.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24619?src=pr&el=h1) Report
> Merging [#24619](https://codecov.io/gh/pandas-dev/pandas/pull/24619?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/19f715c51d16995fc6cd0c102fdba2f213a83a0f?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24619/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24619?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #24619      +/-   ##
==========================================
+ Coverage   92.37%   92.38%   +<.01%     
==========================================
  Files         166      166              
  Lines       52396    52377      -19     
==========================================
- Hits        48403    48388      -15     
+ Misses       3993     3989       -4
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.8% <100%> (ø)` | :arrow_up: |
| #single | `43% <60%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/24619?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/dtypes/missing.py](https://codecov.io/gh/pandas-dev/pandas/pull/24619/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL21pc3NpbmcucHk=) | `92.77% <ø> (-0.42%)` | :arrow_down: |
| [pandas/core/internals/blocks.py](https://codecov.io/gh/pandas-dev/pandas/pull/24619/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzL2Jsb2Nrcy5weQ==) | `94.38% <100%> (+0.16%)` | :arrow_up: |
| [pandas/\_libs/tslibs/\_\_init\_\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/24619/diff?src=pr&el=tree#diff-cGFuZGFzL19saWJzL3RzbGlicy9fX2luaXRfXy5weQ==) | `100% <100%> (ø)` | :arrow_up: |
| [pandas/core/sparse/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/24619/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc3BhcnNlL3Nlcmllcy5weQ==) | `95.53% <100%> (ø)` | :arrow_up: |
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/24619/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `88.09% <0%> (+0.09%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24619?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/24619?src=pr&el=footer). Last update [19f715c...2577c9a](https://codecov.io/gh/pandas-dev/pandas/pull/24619?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/24619?src=pr&el=h1) Report
> Merging [#24619](https://codecov.io/gh/pandas-dev/pandas/pull/24619?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/19f715c51d16995fc6cd0c102fdba2f213a83a0f?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24619/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24619?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #24619      +/-   ##
==========================================
+ Coverage   92.37%   92.38%   +<.01%     
==========================================
  Files         166      166              
  Lines       52396    52376      -20     
==========================================
- Hits        48403    48386      -17     
+ Misses       3993     3990       -3
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.8% <100%> (ø)` | :arrow_up: |
| #single | `43% <60%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/24619?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/dtypes/missing.py](https://codecov.io/gh/pandas-dev/pandas/pull/24619/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL21pc3NpbmcucHk=) | `92.77% <ø> (-0.42%)` | :arrow_down: |
| [pandas/core/internals/blocks.py](https://codecov.io/gh/pandas-dev/pandas/pull/24619/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzL2Jsb2Nrcy5weQ==) | `94.38% <100%> (+0.16%)` | :arrow_up: |
| [pandas/\_libs/tslibs/\_\_init\_\_.py](https://codecov.io/gh/pandas-dev/pandas/pull/24619/diff?src=pr&el=tree#diff-cGFuZGFzL19saWJzL3RzbGlicy9fX2luaXRfXy5weQ==) | `100% <100%> (ø)` | :arrow_up: |
| [pandas/core/sparse/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/24619/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc3BhcnNlL3Nlcmllcy5weQ==) | `95.53% <100%> (ø)` | :arrow_up: |
| [pandas/core/indexes/period.py](https://codecov.io/gh/pandas-dev/pandas/pull/24619/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9wZXJpb2QucHk=) | `92.06% <0%> (-0.06%)` | :arrow_down: |
| [pandas/core/resample.py](https://codecov.io/gh/pandas-dev/pandas/pull/24619/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzYW1wbGUucHk=) | `97.23% <0%> (ø)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24619?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/24619?src=pr&el=footer). Last update [19f715c...e1033e1](https://codecov.io/gh/pandas-dev/pandas/pull/24619?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 this overlaps with #24607 ?  thanks!