4.25.1: support HHVM 4.29+ and current nightlies
Remove fake InvariantException declaration Summary: This was added to get around the inconsistency in how the typechecker and compiler viewed autoimporting. But this should only be enabled in OSS, not WWW. Reviewed By: DavidSnider Differential Revision: D18069991 fbshipit-source-id: ad45b372263bb3003650113bbc9d36229fc80e88