Revert "Finish up mip opts: 2x3 and 3x2"

This reverts commit 88ec28e3d7567ec2c3e26fed66c16a68a8f8ae64.

Reason for revert: <INSERT REASONING HERE>

Original change's description:
> Finish up mip opts: 2x3 and 3x2
> 
> mipmap_build_2048x2047 (2x3):
> sRGB Float Impl (old): 82.9ms (reference)
> 8888                 : 12.3ms (reference)
> sRGB Before          : 61.9ms
> sRGB After           : 53.1ms
> 
> mipmap_build_2047x2048 (3x2):
> sRGB Float Impl (old): 65.9ms (reference)
> 8888 Before          : 10.3ms
> 8888 After           : 8.81ms
> sRGB Before          : 47.8ms
> sRGB After           : 43.5ms
> 
> BUG=skia:
> 
> Change-Id: I53ef01e8b8344f018aa940d6c80cf2cf048bf7fa
> Reviewed-on: https://skia-review.googlesource.com/10028
> Reviewed-by: Brian Osman <brianosman@google.com>
> Commit-Queue: Matt Sarett <msarett@google.com>
> 

TBR=mtklein@google.com,msarett@google.com,brianosman@google.com,reviews@skia.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Change-Id: I3153b75f7f9473057e44ee47ab37421919edaeed
Reviewed-on: https://skia-review.googlesource.com/11289
Reviewed-by: Matt Sarett <msarett@google.com>
Commit-Queue: Matt Sarett <msarett@google.com>
2 files changed