REF: remove unnecessary Block specialization
- [ ] closes #xxxx (Replace xxxx with the GitHub issue number)
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

Broken off from a PR implementing optional 2D support for EAs.  I can't detect any performance difference locally, want to get this in and check the asvs in a few days.
```
mypy (stubtest)..........................................................Failed
- hook id: mypy
- duration: 73.79s
- exit code: 1

/home/runner/work/pandas/pandas/scripts/run_stubtest.py:24: UserWarning: stubtest may fail as 2.1.0rc0+22.gd7b43a57b6 is not a dev version. Please install a pandas dev version or see https://pandas.pydata.org/pandas-docs/stable/development/contributing_codebase.html#validating-type-hints on how to skip the stubtest
  warnings.warn(
pandas._libs.internals.NDArrayBackedBlock is not present at runtime
pandas._libs.internals.NumpyBlock is not present at runtime
pandas._libs.internals.SharedBlock is not present at runtime
``` mypy complaints fixed + green Thanks @jbrockmendel 