AudioService: Don't adjust volume when vol-downing to vibrate or silent

Pressing vol-down to vibrate or silent would (previously) still adjust the
stream volume, setting the last audible volume to 0, which is not allowed
for voice-capable devices.  Thus, the last audible volume would reset to
default on reboot if on vibrate/silent or the lowest volume setting.

By not adjusting volume when vol-downing to vibrate or silent on
voice-capable devices, the last audible volume is always preserved across
reboot.
Revert "frameworks/base: Handle Out of Memory Exception when creating video thumbnails."

This reverts commit 58ac4ce6b0bbde76a666cc12d6e84aea30d371bb.
Revert "Prevent audio players starting on startup."

This reverts commit 16f0954f9b948f2c4a149ff732c17af518845c82.