Revert "service worker: Enable off-the-main-thread service worker script fetch by default"

This reverts commit 7f87468019de69d83e38b291bcfd142445dc1c21.

Reason for revert: This seems to have broken http/tests/devtools/network/network-log-service-worker-navigate.js on WebKit Mac10.13 (retina). https://ci.chromium.org/p/chromium/builders/ci/WebKit%20Mac10.13%20%28retina%29/14412 was the first broken build and right after this landed.

Original change's description:
> service worker: Enable off-the-main-thread service worker script fetch by default
> 
> Note to sheriffs: Feel free to revert this if this breaks something.
> 
> Bug: 924043
> Change-Id: I7164ad621edafebd7fc05d9f4eeee7bd673cbe6a
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1583168
> Commit-Queue: Kenichi Ishibashi <bashi@chromium.org>
> Reviewed-by: Matt Falkenhagen <falken@chromium.org>
> Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#661268}

TBR=falken@chromium.org,kinuko@chromium.org,bashi@chromium.org

Change-Id: Icb6500aba7f6e1f1d80624f95f45a3c318b8262c
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 924043
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1619588
Reviewed-by: Fergus Dall <sidereal@google.com>
Commit-Queue: Fergus Dall <sidereal@google.com>
Cr-Commit-Position: refs/heads/master@{#661285}
1 file changed