Remove NotImplementedError for parse_dates keyword in read_excel
rebase of #12051 and fixes on top

closes #11544
I'll fix the authorship on merge. Thanks for resurrecting this! Not directly an idea about your question (that was the reason I didn't update the PR, as I didn't found the time to dive into the parsers code to figure this out)  # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/15820?src=pr&el=h1) Report
> Merging [#15820](https://codecov.io/gh/pandas-dev/pandas/pull/15820?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/71f621fe11b499a6e1420737faf375ba99bb619b?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `85.71%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/15820/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/15820?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #15820      +/-   ##
==========================================
+ Coverage   90.99%   90.99%   +<.01%     
==========================================
  Files         143      143              
  Lines       49401    49403       +2     
==========================================
+ Hits        44954    44956       +2     
  Misses       4447     4447
```


| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/15820?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/excel.py](https://codecov.io/gh/pandas-dev/pandas/pull/15820?src=pr&el=tree#diff-cGFuZGFzL2lvL2V4Y2VsLnB5) | `79.67% <100%> (ø)` | :arrow_up: |
| [pandas/io/parsers.py](https://codecov.io/gh/pandas-dev/pandas/pull/15820?src=pr&el=tree#diff-cGFuZGFzL2lvL3BhcnNlcnMucHk=) | `95.52% <80%> (ø)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/15820?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/15820?src=pr&el=footer). Last update [71f621f...a1eee67](https://codecov.io/gh/pandas-dev/pandas/pull/15820?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments). @jorisvandenbossche good with this (it all passed ). ? Yes, if it passes the tests, good for me! (but as I said, can't really assess if the changes in the parser code are sensible)