Remove GrBackendObject from tests (except image_from_yuv_textures)

This sets the stage for landing https://skia-review.googlesource.com/c/skia/+/82823 (Update SkImage::MakeFromYUVTexturesCopy to GrBackendTexture)

Change-Id: I2c62f23dc447b9ad55c0b5f06bcd6d7ca0ec4d2b
Reviewed-on: https://skia-review.googlesource.com/83920
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
19 files changed