clean up TODO

The premise of the TODO here is somewhat wrong.  There are other places
where we do pass the destination color space through the ContextRec to
shaders that care... just not here when chosing the top-level blitter.

Change-Id: Ie32cfff5af0328c1280721246194a9eb1f0a5874
Reviewed-on: https://skia-review.googlesource.com/c/174040
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
1 file changed