Hygiene: Remove !important from .flow-revision-content

This class is only used when viewing single revisions of a header
(timestamp link in history page) or a post(not linked afaik).  This
!important selector does not appear to be necessary anymore. Looking
through the git history it was added in the first commit I928373
without explanation.

Bug: T76598
Change-Id: Ie3e90aa4ae4b6f112e03d473344edaba20aaad04
Merge "Hygiene: Remove !important from .flow-revision-content"