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.

Change-Id: I6fd8972e9dd9c578d437245598f2d837bd62085d
Mingle: https://wikimedia.mingle.thoughtworks.com/projects/multimedia/cards/854
Merge "Remove expensive synchronous template validation"