Remove CodecSrc::kIndex8_Always_DstColorType

We have removed support for drawing Index8, so stop testing it in DM.

Bug: skia: 6828
Change-Id: Ib2c4d3ebd371be704151a9f956c0ca2aaf2926a6
Reviewed-on: https://skia-review.googlesource.com/21525
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Leon Scroggins <scroggo@google.com>
3 files changed