Revert "Add String resources for Background User sound notification"

This reverts commit 1fb02e3a.

Reason for revert: <Likely culprit for b/335393084  - verifying through ABTD before revert submission. This is part of the standard investigation process, and does not mean your CL will be reverted.>

Change-Id: I68a5a6a5aa9a30a0c57793047ac890d3399c7f8a