Remove media_session_actions flag

This flag was used as a global override to test behavior launcher in T,
and is no longer needed.

Flag: EXEMPT internal-cleanup
Bug: 254512502
Test: atest LegacyMediaDataManagerImplTest
Test: atest MediaDataProcessorTest
Change-Id: Iec55dece062537f36950203b6f40663096023a9e
5 files changed