[HBD] Remove the "Run all Flash in Allow mode" feature.

We've already removed access to this feature from chrome://flags.

This just removes the now-dead implementing code.

Bug: 709550
Change-Id: I21cd2516874722525c2ddab4a2ab0840e46d38c4
Reviewed-on: https://chromium-review.googlesource.com/580363
Reviewed-by: Bernhard Bauer <bauerb@chromium.org>
Commit-Queue: Tommy Li <tommycli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#488683}
3 files changed