[IOS][Omnibox] Remove dealloc from OmniboxPopupRowTrailingButton

This CL refrains from removing the observation of the notification on
dealloc. As this done automatically.

Fixed: 443452716
Change-Id: I7fb838557beac4c20cce1681ea461ea8b50ef8e9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6921613
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Ameur Hosni <ameurhosni@google.com>
Auto-Submit: Ameur Hosni <ameurhosni@google.com>
Cr-Commit-Position: refs/heads/main@{#1512350}