Finalization: remove AIDL_FROZEN_REL

Whether unfrozen interfaces are used is determined
by the release configuration. This causes our CI
behavior to match our normal build/test behavior.
Effectively, unfrozen HALs are allowed for
development at any time, but they can only be used
on trunk*.

Bug: 417308295
Test: N/A
Change-Id: I77e17a55758cbbbe9c80e4ba506f76fced43d474