Revert "BUG: first("1M") returning two months when first day is last day of month"
Reverts pandas-dev/pandas#38331
known test failure

```
=========================== short test summary info ============================
FAILED pandas/tests/io/test_html.py::TestReadHtml::test_banklist_url_positional_match[bs4]
= 1 failed, 146315 passed, 3162 skipped, 1095 xfailed, 66 warnings in 2648.26s (0:44:08) =
```