refactor SkColorSpaceXform a bit

I was having trouble reading my way through this code,
so I decided it needed a little weedwhacking.

The main thrust here is:
  - remove completely pointless ColorSpaceMatch templating
  - remove absurdly paranoid public/protected/private/friend
    relationships

This is still about twice as overdesigned as I'd like...

Change-Id: I275ddbe028ebb09ed383ed7bfaba394975eea27a
Reviewed-on: https://skia-review.googlesource.com/55260
Commit-Queue: Mike Klein <mtklein@chromium.org>
Reviewed-by: Brian Osman <brianosman@google.com>
3 files changed