Remove from start/end dates if tz is not None (remove check of inferred_tz).
DOC: mention that stack/unstack implicitly sort
DOC: mention implicit sorting in docstrings
ENH: tz_localize(None) allows to reset tz
Merge pull request #7852 from sinhrks/reset_tz

ENH: tz_localize(None) allows to reset tz
Merge pull request #7937 from toobaz/stack_unstack_doc

DOC: mention that stack/unstack implicicly sort
Merge pull request #7909 from rockg/master

Remove from start/end dates if tz is not None (#7901, #7835)