Remove WrappedObject::retain. With resources being mostly deleted by the Renderer along with a serial number, the retain move semantics weren't very useful. Refactoring change only. BUG=angleproject:2200 Change-Id: I7b72b1decfa7604cdd767e7d9b5213b9383eb240 Reviewed-on: https://chromium-review.googlesource.com/742369 Reviewed-by: Geoff Lang <geofflang@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>