Backport PR #38679 on branch 1.2.x (Revert "Deprecated casting an object-dtype index of datetime objects to DatetimeIndex in the Series constructor (23598)")

[meeseeksmachine]

Backport PR #38679: Revert "Deprecated casting an object-dtype index of datetime objects to DatetimeIndex in the Series constructor (23598)"

[simonjayhawkins]

same failure seen on another PR (before PR this is backporting was merged to master)

=========================== short test summary info ============================
FAILED pandas/tests/arrays/categorical/test_warnings.py::TestCategoricalWarnings::test_tab_complete_warning
FAILED pandas/tests/frame/test_api.py::TestDataFrameMisc::test_tab_complete_warning[DataFrame]
FAILED pandas/tests/frame/test_api.py::TestDataFrameMisc::test_tab_complete_warning[Series]
FAILED pandas/tests/indexes/test_base.py::TestIndex::test_tab_complete_warning
FAILED pandas/tests/resample/test_resampler_grouper.py::test_tab_complete_ipython6_warning
= 5 failed, 145317 passed, 4090 skipped, 1091 xfailed, 6 warnings in 874.50s (0:14:34) =