Clean up code for the flag `use_playback_info_for_routing_controls`.

Fix: 409611629
Flag: EXEMPT removing flag use_playback_info_for_routing_controls
Test: atest com.android.settingslib.media.InfoMediaManagerTest,
atest com.android.systemui.media.dialog.MediaSwitchingControllerTest,
atest com.android.systemui.media.controls.domain.pipeline.MediaDeviceManagerTest

Change-Id: I67aa2a62b4ebefcebc02fc06b181acee4d4846ae