Fix deleting pages/files when using Microsoft SQL Server

Fix deleting pages/files when using Microsoft SQL Server

Right now we have a slew of foreign key violations whenever we try to
delete something due to the way MediaWiki handles page
deletions. Let's remove those foreign keys from places where IDs are
maintained even though the records they are pointing to have been deleted.

Also, work has begun on the massive (re)naming of every constraint in the
schema, so that icky hacks like those employed in these patch files don't
need to be used in the future; rather, we can simply refer to the
constraints by name.

Change-Id: I79938d36a8e35debd3e27052d8ef0e3e6c32f40c