Revert "service worker: Add virtual tests for on-the-main-thread script fetch"

This reverts commit 971acfcbf68b2d81d5e531fd62907bbdc1197c65.

Reason for revert:

Findit (https://goo.gl/kROfz5) identified CL at revision 671864 as the
culprit for flakes in the build cycles as shown on:
https://analysis.chromium.org/p/chromium/flake-portal/analysis/culprit?key=ag9zfmZpbmRpdC1mb3ItbWVyQwsSDEZsYWtlQ3VscHJpdCIxY2hyb21pdW0vOTcxYWNmY2JmNjhiMmQ4MWQ1ZTUzMWZkNjI5MDdiYmRjMTE5N2M2NQw

Sample Failed Build: https://ci.chromium.org/buildbot/chromium.linux/Linux%20Tests%20%28dbg%29%281%29/81349

Sample Failed Step: webkit_layout_tests

Sample Flaky Test: virtual/not-omt-sw-fetch/external/wpt/service-workers/service-worker/fetch-canvas-tainting-video.https.html

Original change's description:
> service worker: Add virtual tests for on-the-main-thread script fetch
> 
> On-the-main-thread script fetch is disabled by default. Add virtual
> tests for on-the-main-thread script fetch to have better test
> coverage until we ship off-the-main-thread script fetch.
> 
> Bug: 967272
> Change-Id: If0b50ad557699d57bae70b2972418df5dc91ed72
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1673487
> Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
> Commit-Queue: Kenichi Ishibashi <bashi@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#671864}


Change-Id: I95b54ba1e51139180ba860f5d9c73aff33995276
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 967272
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1675467
Cr-Commit-Position: refs/heads/master@{#671972}
4 files changed