Remove expensive synchronous template validation
In 1.25 the async parameter gets deprecated. This very advanced
feature requires such deep knowledge of how Commons works
that I believe the users who know about it don't really need the
validation. Furthermore, the worst case scenario is just that junk
gets added to a section of the file page's wikitext by a user not
knowing what they're doing. Which doesn't seem like a big deal, since
it can always be fixed after publication.