Guard to remove kIndex_8_SkColorType

Bug: skia:6828
Change-Id: Ia942a36abb18213184f8d436555a658270d97d47
Reviewed-on: https://skia-review.googlesource.com/22721
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Florin Malita <fmalita@chromium.org>
Reviewed-by: Herb Derby <herb@google.com>
29 files changed