Release audio record when mirroring ends

This change replaces stop() with release (which includes a stop under
the hood). This is necessary to ensure resources are freed.

Bug: b/362507305
Test: atest CtsMediaRouterTestCases:android.media.router.cts.SystemMediaRoutingTest
Flag: com.android.media.flags.enable_mirroring_in_media_router_2
Change-Id: Ia0c60fb69144a368c1c279bc4989c2b2e0f6fe6a