TST: fixes for 2.6 comparisons
Revert "Merge pull request #7591 from mcwitt/parse-index-cols-c"

This reverts commit 2c603e17b60665b5db6b373f33e1479f47b7155a, reversing
changes made to 49a86f1fb90ea199cba0954ede6b939f672867b1.
PERF: allow dst transition computations to be handled much faster
      if the end-points are ok (GH7633)
PERF: allow slice indexers to be computed faster
Merge pull request #7652 from jreback/dst_transitions

PERF: fix perf issue in tz conversions w/o affecting DST transitions
API: disallow inplace setting with where and a non-np.nan value (GH7656)
Merge pull request #7657 from jreback/where

API: disallow inplace setting with where and a non-np.nan value (GH7656)
BUG: DatetimeIndex.delete with tz raises ValueError
Merge pull request #7608 from sinhrks/delete2

BUG: DatetimeIndex.delete with tz raises ValueError