clean up S16CPU

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>
6 files changed