Revert "Deprecated casting an object-dtype index of datetime objects to DatetimeIndex in the Series constructor (23598)"
This **partially** reverts commit 90a61350b1be7a200238212bd8d118a25a4d3d95.

- [ ] closes #38182
- [ ] tests added / passed
- [ ] passes `black pandas`
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry
