FaceGaze: remove polling from tests

Bug: b:309121742
Change-Id: Ie33762bc34f43eb227ae19ec8c91f4db7f45557e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5332139


Commit-Queue: Akihiro Ota <akihiroota@chromium.org>
Reviewed-by: Katie Dektar <katie@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1267481}