remove RGB_888x pixel tests exceptions.
remove RGB_888x pixel tests exceptions.

Should have been removed with
https://skia.googlesource.com/skia/+/974c821502042c0ab233affb0f38bf2b49f5ecfe

Bug: skia:8862
Change-Id: I3e6445a006165cc2d5713c4b21b23ed674c0a6fe
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/405399
Reviewed-by: Robert Phillips <95e8ac5504948c7bf91b22c16a8dbb7ae7c66bfd@google.com>
Commit-Queue: Brian Salomon <61fabaaf0876044aeedfd8e351e485c028d69e7b@google.com>

google/skia,google/skia,google/skia,google/skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,google/skia,google/skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia