frameworks/base: Remove CM headset/speaker volume restore code

- Jelly Bean already has this built in for the media volume stream, but it's
broken by having our own code in there as well.
Other audio streams will no longer have their volume levels restored, and only
media volume will be subjected to the 'safe headset volume restore' cap.

- Cleaned up the 'link notification with ringtone volume' code.

Change-Id: I06e1d159a66e2d6c09c6128c4c946d9578ea90cd