audio: Do not use StreamSwitcher for StreamRemoteSubmix

Since use of StreamSwitcher causes the worker thread to be changed
during connected device change, its use must be avoided. We intend
to remove StreamSwitcher completely in future.

Bug: 300130515
Bug: 338974476
Bug: 368723297
Bug: 369272078
Bug: 369289912
Bug: 369964381
Test: atest CtsMediaAudioTestCases
Test: atest VtsHalAudioCoreTargetTest
Change-Id: I4f6fd35f69d73641a86e1102f1d30d5e8f626e8f