[iOS] Removes CloseAllTabs implementation

This CL removes CloseAllTabs confirmation implementation.

Bug: 1240947
Change-Id: Ia92c606a5dd21ba0e20c8e66a075e1a3813bc710
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3113805


Commit-Queue: Ewann Pellé <ewannpv@chromium.org>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Max Curran <curranmax@chromium.org>
Reviewed-by: Mohammad Refaat <mrefaat@chromium.org>
Cr-Commit-Position: refs/heads/main@{#915897}