Remove unrefed texture validation variables. These were causing unused variable warnings in Linux GCC builds. BUG=angle:773 Change-Id: I860d425a1caef07a58f6ff1b6c113ad7b63283dc Reviewed-on: https://chromium-review.googlesource.com/231856 Tested-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Kenneth Russell <kbr@chromium.org>