[iOS][Omnibox] Cleanup shortcuts suggestion flag

Remove iOS shortcuts suggestions flag after launch.

Bug: None
Change-Id: Iae9470d6df8e887a574f014bac338b566c4f65b3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5613293


Auto-Submit: Christian Xu <christianxu@chromium.org>
Commit-Queue: Christian Xu <christianxu@chromium.org>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Reviewed-by: manuk hovanesian <manukh@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1312816}