CrOS Bluetooth: Cleanup Jelly flag logic in bluetooth pairing dialog

Jelly has launched and this conditional code can be cleaned up. Also
removes associated tests.

Bug: b:319740292
Test: Manually verify dynamic colors supported in dialog
Change-Id: I3fc5be5afd8f9e8bdce4e8b01a12de6049d35eb6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5411311


Reviewed-by: Chad Duffin <chadduffin@chromium.org>
Commit-Queue: Wes Okuhara <wesokuhara@google.com>
Reviewed-by: Jason Zhang <jiajunz@google.com>
Cr-Commit-Position: refs/heads/main@{#1282147}