Remove IsAccessCodeCastFreezeUiEnabled from backend implementation.

This check does not work when casting is started from the ChromeOS quick
settings. We will prefer to experiment gate the feature from the
frontend implementation as that will be the only route that calls these
fuctions

Bug: b/277956799
Change-Id: I96b69908d8bebf5155e247b462c604a48bcdc078
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4421631
Reviewed-by: Jordan Bayles <jophba@chromium.org>
Commit-Queue: Dorian Brandon <dorianbrandon@google.com>
Auto-Submit: Dorian Brandon <dorianbrandon@google.com>
Code-Coverage: Findit <findit-for-me@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1130068}