This should prevent further unexpected bot breakage due to
unreferenced variables in the ASSERT expression.

Also remove the no longer needed variable referencing macro.

BUG=angleproject:1586

Change-Id: I127695165bdfe39c51fe8d17e00daf6bf2fa8252
Reviewed-on: https://chromium-review.googlesource.com/404948Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>