[Media Notification] Remove source icon observer

We do not actually display source icons because the
notification has a colored background and this causes
favicons to clash. We should remove the icon observer
so we do not incorrectly show them.

BUG=979232

Change-Id: Ibaa274a4b0deecf49eda5b8d52482ff3627f5a9d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1680785
Commit-Queue: Becca Hughes <beccahughes@chromium.org>
Reviewed-by: Tommy Steimel <steimel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#673093}
5 files changed