media.log cleanup

Remove almost all of the specific logs, but leave the media.log
logging infrastructure in place for the next time we need it.

Re-apply a few good changes that were reverted earlier:
 - check logf format vs. argument list compatibility
 - distinguish potentially modified and actually modified tracks in FastMixer
 - fix benign bug where sq->end() was called more than once
 - fix a build warning

Bug: 6490974
Change-Id: I02d3e83646c738acaebb415bd0d6b548638b4ef5