Remove force-dark-mode flag on ChromeOS.

Enabling the flag appears to break rendering of most pages on ChromeOS,
including chrome://flags. This CL removes the option to enable it for
now.

Bug: 1011696
Change-Id: I818be2add7c34e181297477244805e02f7ffcb85
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1848478
Reviewed-by: Dominic Mazzoni <[email protected]>
Commit-Queue: Aran Gilman <[email protected]>
Cr-Commit-Position: refs/heads/master@{#706524}
1 file changed