Remove unused APIs and skin_detection dead code

This removes the unused spatial scalability, temporal layers, and svc
parameters from the aom API. There is no code implementing these APIs,
and if it they are needed in the future, just resurrect them from this
commit. The skin_detection code is unused and won't be used.

Change-Id: I3185bad6ec58c55426953b658a12a06ed041d7cd
11 files changed