remove MIPS DSP optimizations

There are only a couple of these, primarily focused on index8 srcs and 565 dsts.  The burden's starting to outweigh the benefit.  No one on the team knows MIPS assembly.

If we're going to try this again, I'd rather we try some sort of SkNx / compiler-intrinsic based approach, probably targeting MIPS SIMD (MSA), not this older instruction set.

We already ignore these files for 64-bit MIPS.  This just closes the loop on 32-bit MIPS.

CQ_INCLUDE_TRYBOTS=skia.primary:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD,Build-Ubuntu-Clang-mips64el-Debug-Android,Build-Ubuntu-Clang-mips64el-Release-Android,Build-Ubuntu-Clang-mipsel-Debug-Android,Build-Ubuntu-Clang-mipsel-Release-Android

BUG=skia:6065

Change-Id: Iecac15b56f59625b2e743ea36e7791b90bb0b422
Reviewed-on: https://skia-review.googlesource.com/6353
Reviewed-by: Leon Scroggins <scroggo@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
7 files changed