Revert^2 "Add MODIFY_AUDIO_SETTINGS_PRIVILEGED permission check to volume callback"

This reverts commit b1ca8f99.

Reason for revert: Reintroduce work with flag guard

Bug: 402502314
Test: m -j on auto/clockwork devices
Flag: android.media.audio.register_volume_callback_api_hardening
Change-Id: I62ba6e1a2b72c4fc67708ff319adca1ee990be96