Remove obsolete kIndex_8_SkColorType reference

Bug: skia:6828

No public API change. Just removing an obsolete comment.
TBR=reed@google.com

Change-Id: I6c729c62bf7d94fc6acb677d68e7091f80d73b3e
Reviewed-on: https://skia-review.googlesource.com/150781
Commit-Queue: Leon Scroggins <scroggo@google.com>
Reviewed-by: Leon Scroggins <scroggo@google.com>
1 file changed