Revert "hal: add custom platform abstraction"

* Handle this in a more extensible way with upcoming platform info
  extension code.

This reverts commit 36a435d08826160ddbf9e0759711f7badae42566.

Change-Id: I9683e27b70f591bff6c5131523ef7c3e51ee6513
Revert "hal: Add speaker backend case handling"

* Handle this in a more extensible way with upcoming platform info
  extension code.

This reverts commit 957c3d94bf34da538b3cd296e17b94a9206fd8d1.

Change-Id: Ie0b86bfd8decd92bda76a2706e5ebd7dcedae89b