Update last gm to use sampling, hide legacy api

persp_shaders_ gm expected diff (in gpu backends only), due to change
from filterquality (which gpu and cpu interpreted differently for mips)
to samplingoptions (which both backends interpret the same).

Specifically for kMedium:
- gpu treated as SkMipmapMode::kLinear
- cpu treated as SkMipmapMode::kNearest

Bug: skia: 7650
Change-Id: Idc53ad8d01d9c928b425c092b36191153714d347
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/343737
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
3 files changed