[Messaging] Clear tab removed message cards on sign out

When the user signs out, currently the backend doesn't issue
hide persistent messages to observers. Hence we see various
"tab group removed" messages on the tab groups pane.
This CL listens to the sign out event and clears out the
surface.

Bug: None
Change-Id: I0d9dc4bb8f36722d04f4352a171101ff78cf1d17
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6295043
Reviewed-by: Sky Malice <skym@chromium.org>
Commit-Queue: Shakti Sahu <shaktisahu@chromium.org>
Reviewed-by: Calder Kitagawa <ckitagawa@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1424194}