video: Remove tast prefix in test name

Remove the prefix for correct syntax in expectation for
av1_files_from_bugs_346405213 to fail on skyrim.

BUG=b:477358641
TEST=none

Change-Id: I04ebf20a83c447f3aa3f848fed0ffb1f1deda32b
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/graphics/+/7520475
Commit-Queue: Hang Nguyen <hnt@google.com>
Tested-by: Hang Nguyen <hnt@google.com>
Auto-Submit: Hang Nguyen <hnt@google.com>
Reviewed-by: Nathan Hebert <nhebert@chromium.org>