universal8890: clean up mixer_paths_0

 * mixer_paths_0 is built by merging together stock mixer_gains and
   mixer_paths, and then by manually writing OSS Samsung HAL routes,
   exploiting stock paths.

 * when we firstly built the mixer_paths_0 we pulled stock mixer_paths
   and mixer_gains in their entirety, only adding OSS Samsung HAL
   routes.
   A lot of paths though are dead as they are not used by OSS HAL.

 * Remove those dead paths to avoid confusion when editing mixer_paths_0
   and to keep it clean.

Change-Id: Ic0d2a94d8c84cf0b28e355d57bd82b81043fdda4