ERR: Raise the correct error for to_datetime()
- [x] closes #23830
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

Verified that it does not affect the fixes by #19529 (for issue #19382)
Hello @varadgunjal! Thanks for updating the PR.



Cheers ! There are no PEP8 issues in this Pull Request. :beers: 

##### Comment last updated on December 24, 2018 at 17:22 Hours UTC # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23969?src=pr&el=h1) Report
> Merging [#23969](https://codecov.io/gh/pandas-dev/pandas/pull/23969?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/fc7bc3f74d1f5702bf66c519ad190126538a8f5b?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/23969/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/23969?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #23969   +/-   ##
=======================================
  Coverage    92.3%    92.3%           
=======================================
  Files         163      163           
  Lines       51943    51943           
=======================================
  Hits        47946    47946           
  Misses       3997     3997
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.71% <ø> (ø)` | :arrow_up: |
| #single | `43% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23969?src=pr&el=continue).
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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23969?src=pr&el=footer). Last update [fc7bc3f...6aa0bf3](https://codecov.io/gh/pandas-dev/pandas/pull/23969?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 can you merge master Apologies for the tardiness. I got slightly caught up with coursework. can you merge master. Done Once whitespace and test comments from jreback and gfyoung are addressed, lgtm. can you merge master Closing as stale. Ping if you'd like to continue Revived in #25467