[iOS][CBD] Only save prefs when user goes through with the deletion

This CL only updates the clear browsing data option prefs when the user
actually goes through the deletion. This aligns the behaviour with
Desktop. In future, Android will also follow the same logic.

Bug: 331757949
Change-Id: I585505872f4a2c24373650df3d349aafa4deb563
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5401669


Reviewed-by: Arthur Milchior <arthurmilchior@chromium.org>
Commit-Queue: Filipa Senra <fsenra@google.com>
Reviewed-by: Ewann Pellé <ewannpv@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1283151}