[iOS] Don't hide TabGroup if the TabGrid has been reopened

If the TabGrid has been reopened before the end of the exit animation,
don't hide the TabGroup to ensure that the animation to open an
existing tab group isn't broken.

Also, remove an unnecessary call to hide TabGroup in the TabGrid
coordinator. It is already part of the completion block.

Bug: 432227955
Change-Id: Ic8ceffce112b29f83d792cd9dfa4160d424bdd58
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6771786
Reviewed-by: Ewann Pellé <ewannpv@chromium.org>
Commit-Queue: Ewann Pellé <ewannpv@chromium.org>
Auto-Submit: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1489500}