Revert "Add kR8_unorm_SkColorType"

This reverts commit 3225c8cc46890bbd0ecf8893db204ee77ecb28a1.

Reason for revert: Client code needs to handle the new enum value.

Original change's description:
> Add kR8_unorm_SkColorType
>
> Change-Id: I97b5bc7f90715664f233ca7b7c41c0ecbfc29ac4
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/505679
> Reviewed-by: Michael Ludwig <michaelludwig@google.com>
> Reviewed-by: Greg Daniel <egdaniel@google.com>
> Commit-Queue: Brian Osman <brianosman@google.com>

Change-Id: I1174f533600827e29131198c10c243d9cf1300ae
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/506457
Auto-Submit: Brian Osman <brianosman@google.com>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
32 files changed