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DidDetach wasn't getting called and there was no receiver for the
message anymore. So all of this code is dead. Remove it.

BUG=993189,533069

Change-Id: I71b712fd0f21a89ab60cd1c509afbb6e02604a23
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2505126Reviewed-by: Ken Buchanan <kenrb@chromium.org>
Reviewed-by: Kevin McNee <mcnee@chromium.org>
Reviewed-by: James MacLean <wjmaclean@chromium.org>
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#821839}