Bug 831236: remove mobile/xul, r=axel,mfinkle,gps,glandium

--HG--
extra : rebase_source : be789eac5e8e769a54e6c0c4126065c8b5a5192e
Bug 817448: remove MozBlobBuilder from FrameWorker API, r=mixedpuppy
Bug 831236 followup: adjust comment