resourceloader: Remove redundant check in mw.loader.store for Opera 12

resourceloader: Remove redundant check in mw.loader.store for Opera 12

Opera 12 is no longer supported for Grade A. This regex was currently
running on every module script executed on every page in between
each module's execution.

execute() for module A -> handlePending -> mw.loader.store.set()
-> Opera 12 check -> schedule update -> yield to module B.

The serialisation logic in store.set() should probably more
generally deferred and taken out of this path, but until then,
every bit helps.

Change-Id: I8d4628b6d663fe25040c6ef0b4983a4b7eea94c6