Remove TabModelSelector obsever when ChromeTabbedActivity destroyed

ChromeTabbedActivity adds the observer to TabModelSelector when it creates the tab model. But it never calls removeObserver on TabModelSelector when it is destroyed.
This CL will remove the obsever from TabModelSelector when ChromeTabbedActivity destroyed.

Bug: 40949112
Change-Id: I107b6dc4fabaf4774b0689b297c0bd2201129dd9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5737030
Reviewed-by: Sky Malice <skym@chromium.org>
Reviewed-by: Calder Kitagawa <ckitagawa@chromium.org>
Commit-Queue: Calder Kitagawa <ckitagawa@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1332363}