This assertion is causing problems on the debug bots.  While the assertion is
nice for local debugging, causing the entire run of WebGL cts on the trybots
to fail is too big of a drawback.

BUG=angleproject:889

Change-Id: Ie86d2f0e84132bef8fb94a693440af7e9b7fc8e9
Reviewed-on: https://chromium-review.googlesource.com/314480Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>