Remove obsolete Trebuchet config overlay

These config settings are no longer present in the Launcher3-derived
Trebuchet and will break the build once that's enabled.

Change-Id: Ie76bf33a3e8d92a2b07672b453077ca5691330fc
Update audio prebuilts to use Thumb instructions

This saves 168 KB in the installed image and should have zero to
slightly positive impact on performance.

Change-Id: Ice4da0bab81de6136a1533a6b1aca1d393854ffd