Revert "audio: allow standby for direct track"

This reverts commit 9cd7ad10.

Prior CL allows Direct PCM tracks to enter standby on pause
which unfortunately causes timestamp frame position to reset to 0.

Test: Audio sanity test
Test: Verified in bug to remove the regression above.
Bug: 157609403
Change-Id: I5e0d43a0e50981a300bc05711b71efe0b7e22f98