Revert "Add support for system-wide mirroring"

This reverts commit fc62ef1c.

Reason for revert: We don't want to support global routing for the first iteration.

Test: atest CtsMediaRouterTestCases:android.media.router.cts.SystemMediaRoutingTest
Bug: b/362507305
Bug: b/413313659
Change-Id: Ic4f1d01f630f3872634ff604fadc42bdafbf71a6