Remove "WritableFiles" runtime enabled flag

Removing a flag added accidentally at
https://crrev.com/fb8ff28be837c61b79916d1bc79399b0fe51188b.

Bug: None
Change-Id: I9e9ec74930849f94c94d52c28e610d337c23332e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1578725
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Auto-Submit: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#653182}
1 file changed