Revert change to comparison op with datetime.date objects
- [x] closes #21152
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

cc @jbrockmendel, @innominate227

FYI, @jorisvandenbossche the whatsnew will conflict with your other PR
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21361?src=pr&el=h1) Report
> Merging [#21361](https://codecov.io/gh/pandas-dev/pandas/pull/21361?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/7f6ea676808a39801e1d36ec1db48f269fa4e5a9?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/21361/graphs/tree.svg?token=eZ4WkYLtcO&width=650&src=pr&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/21361?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #21361      +/-   ##
==========================================
+ Coverage   91.89%   91.89%   +<.01%     
==========================================
  Files         153      153              
  Lines       49579    49590      +11     
==========================================
+ Hits        45559    45570      +11     
  Misses       4020     4020
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.29% <100%> (ø)` | :arrow_up: |
| #single | `41.85% <36.36%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/21361?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/ops.py](https://codecov.io/gh/pandas-dev/pandas/pull/21361/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvb3BzLnB5) | `96.41% <100%> (+0.05%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21361?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/21361?src=pr&el=footer). Last update [7f6ea67...174c458](https://codecov.io/gh/pandas-dev/pandas/pull/21361?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @TomAugspurger This is ready? IMO, yes. I didn't change the quoting in the docs, since https://github.com/pandas-dev/pandas/issues/19750 hasn't been resolved (just replied there).