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The feature has been successfully enabled by default, so this CL removes
it, as well as the favicon cleanup logic for pseudo-USS introduced by
https://crrev.com/c/1917173.

Bug: 978775
Change-Id: I8539cda6166e6a03e434b9545278b7b6abda3a19
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2089823
Commit-Queue: Victor Vianna <victorvianna@google.com>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#747687}