Remove paletted source support

This was never used by anyone.

Effectively reverts: https://skia-review.googlesource.com/c/skcms/+/163170

Bug: skia:8473
Change-Id: Iaa137c9661d7cfc4599d074b3323e56d7bd3b0e5
Reviewed-on: https://skia-review.googlesource.com/c/skcms/+/770576
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Leon Scroggins <scroggo@google.com>
6 files changed