Don't store colortables in pixmaps or pixelrefs

Lots more changes coming later (need to remove colortable parameters from bitmaps and pixmaps)

Bug: skia:6828
Change-Id: Ic63e89570644839fab068141f49915b3f66d1053
Reviewed-on: https://skia-review.googlesource.com/24127
Reviewed-by: Leon Scroggins <scroggo@google.com>
Commit-Queue: Mike Reed <reed@google.com>
6 files changed