Remove pandas workaround in `_roll_series_with_gap`

[tamargrey]

In #1770, a workaround had to be added for the following pandas bug pandas-dev/pandas#43016. This bug has been fixed and will be released as a part of pandas 1.4.0 release.

Once 1.4.0 is out and we're okay with upping our min requirement, we can remove the workaround.

[gsheni]

This will require #1771