Bug 1794217 [wpt PR 36346] - [Fixit] Clean up redundant executor HTML files., a=testonly

Bug 1794217 [wpt PR 36346] - [Fixit] Clean up redundant executor HTML files., a=testonly

Automatic update from web-platform-tests
[Fixit] Clean up redundant executor HTML files. (#36346)

Now that we have /common/dispatcher/remote-executor.html, these are no
longer needed. There remain a fair number of custom executors, but those
all perform some additional work compared to the common executor.

Also extract a helper to compute the URL of the common executor and use
it instead of manually concatenating URLs in most places.

Bug: chromium:1273818
Change-Id: I0c9211b9775f280dbf3ab7ed1f6c5dd80bef6229
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3937933
Reviewed-by: Arthur Sonzogni <arthursonzogni@chromium.org>
Auto-Submit: Titouan Rigoudy <titouan@chromium.org>
Commit-Queue: Arthur Sonzogni <arthursonzogni@chromium.org>
Commit-Queue: Titouan Rigoudy <titouan@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1056318}

Co-authored-by: Titouan Rigoudy <titouan@chromium.org>
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wpt-commits: 55b88b026c259b71f24eb751f45b70895f2e70e2
wpt-pr: 36346