Replace 'sanity check' keyword in Assistant files

See go/inclusive-codebase.

Bug: b/161801556
Test: Local compile
Change-Id: I6f489e910c4050dab71b2d2bc30fdfb6679fb6bc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2316450


Auto-Submit: Yue Li <updowndota@chromium.org>
Reviewed-by: Jeroen Dhollander <jeroendh@chromium.org>
Commit-Queue: Yue Li <updowndota@chromium.org>
Cr-Commit-Position: refs/heads/master@{#791469}