De-duplicate masking/fallback logic in ops
Some nice deletions here.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19613?src=pr&el=h1) Report
> Merging [#19613](https://codecov.io/gh/pandas-dev/pandas/pull/19613?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/b83512773ab0dd3908cf2ef5ccaddcd8e0337c64?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `96%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/19613/graphs/tree.svg?height=150&width=650&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/19613?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #19613      +/-   ##
==========================================
- Coverage   91.62%    91.6%   -0.02%     
==========================================
  Files         150      150              
  Lines       48790    48795       +5     
==========================================
- Hits        44703    44701       -2     
- Misses       4087     4094       +7
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.98% <96%> (-0.02%)` | :arrow_down: |
| #single | `41.74% <8%> (+0.01%)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/19613?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/19613/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.16% <ø> (-0.27%)` | :arrow_down: |
| [pandas/core/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/19613/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc2VyaWVzLnB5) | `94.56% <100%> (-0.05%)` | :arrow_down: |
| [pandas/core/ops.py](https://codecov.io/gh/pandas-dev/pandas/pull/19613/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvb3BzLnB5) | `96.83% <95.83%> (+1.61%)` | :arrow_up: |
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/19613/diff?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `65.22% <0%> (-1.74%)` | :arrow_down: |
| [pandas/core/dtypes/dtypes.py](https://codecov.io/gh/pandas-dev/pandas/pull/19613/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZHR5cGVzL2R0eXBlcy5weQ==) | `96.08% <0%> (ø)` | :arrow_up: |
| [pandas/io/formats/format.py](https://codecov.io/gh/pandas-dev/pandas/pull/19613/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvZm9ybWF0LnB5) | `96.25% <0%> (+0.01%)` | :arrow_up: |
| [pandas/core/groupby.py](https://codecov.io/gh/pandas-dev/pandas/pull/19613/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ3JvdXBieS5weQ==) | `92.2% <0%> (+0.07%)` | :arrow_up: |
| [pandas/core/arrays/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/19613/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYXJyYXlzL2Jhc2UucHk=) | `60.6% <0%> (+3.93%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19613?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/19613?src=pr&el=footer). Last update [b835127...221f8a6](https://codecov.io/gh/pandas-dev/pandas/pull/19613?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks!