rm GaussNewton.[ch]

Move its impl back into TransferFunction.c, rewrite internal APIs
a little to reflect that it's always calling rg_nonlinear().

Change-Id: I4a2dacbc3efaa0d7456dcdc7467c9095e498c243
Reviewed-on: https://skia-review.googlesource.com/128932
Commit-Queue: Mike Klein <mtklein@chromium.org>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: Mike Klein <mtklein@chromium.org>
Reviewed-by: Brian Osman <brianosman@google.com>
6 files changed