Remove two YUV effect GMs: yuv_to_rgb_effect and yuv_nv12_to_rgb_effect.

These aren't testing anything that isn't tested more thoroughly in other
GMs. This avoids having to update them as SkYUVAInfo is used more broadly
in the GPU backend.

Bug: skia:10632
Change-Id: Id02604863f437666005b410213f5970426f1fa8e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/335659
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>

Author: bsalomon