Remove .sub flag from WebTransport tests

After moving the URL variables into
resources/webtransport-test-helpers.sub.js in [1], it is unnecessary to
still have the .sub test type flag in some test file names as they do
not directly use the server-side substitution feature[2] anymore.

[1] https://chromium-review.googlesource.com/c/chromium/src/+/3134980
[2] https://web-platform-tests.org/writing-tests/server-pipes.html#sub

Bug: 1201569
Change-Id: Ib7d4377bb8b82907338b08ac178e2535a682d13f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3144591
Reviewed-by: Adam Rice <[email protected]>
Commit-Queue: Nidhi Jaju <[email protected]>
Cr-Commit-Position: refs/heads/main@{#918695}

Author: nidhijaju