SkColorSpace cleanup

Remove SkColorSpace_XYZ, no need for an interface with one
implementation.

Change-Id: I47a23293334b5e02a6e5af8356b3df0262f86d5a
Reviewed-on: https://skia-review.googlesource.com/150138
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
9 files changed