[ Merge of http://go/wvgerrit/142229 and http://go/ag/16147655 ] This adds concurrency protection to a session when keys or a license is removed from a session. Bug: 195625322 Test: GtsMediaTestCases, unit/integration tests, YT EME conformance test Change-Id: I38601a58dc593ce053cb5457b9d42d2c35f3f041