Extensions: Remove assert usages on test names

These asserts are obsolete because these tests are now using TypeScript, which will throw a compiler error if the test does not exist.

Bug: 1291526
Change-Id: I88bfddf58701572782a91ff71d1c42d90c3a2eb9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4029660


Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Commit-Queue: Cole Horvitz <colehorvitz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1072415}