remove error logging from user (release) builds

this leaves it forced on in debugging variants.

ps2: define ERROR_DISABLED 0 by default, then set to 1 if USER_VARIANT

Change-Id: I5fb84371b65bd9c327fe34ea93f723ad64295e6f
Enable Webworkers and GC fix

Cherrypicked from Iad989ce9378c24e250827533cfc698f2e76c3be7 (#/c/157027)

Change-Id: Ib779906e3354bb541d47c7f1096e3faa611c65a7