S16CPU is used only inside Skia, and only sparsely.
- SkRandom::nextS16() and nextU16() were used rarely enough
that it makes things simpler to get rid of them.
- SkAlphaBlend255() was unused outside tests.
- SkIntToFDot6() looks like it really wants to take an int.
Change-Id: I3ca773beb6c04c691947d4602f27c819b660554d
Reviewed-on: https://skia-review.googlesource.com/151700
Reviewed-by: Brian Osman <brianosman@google.com>