Revert "Reimplement TwoPointConicalGradient_gpu"

This reverts commit 84f18c422ae98085c452d3f721ec32228e92f531.

Reason for revert: GMs are incorrect on some mobile devices

Original change's description:
> Reimplement TwoPointConicalGradient_gpu
> 
>     4.24% faster in gradient_conical_clamp_shallow_dither
>     6.43% faster in gradient_conicalOutZero_clamp_hicolor
>    10.41% faster in gradient_conicalOut_clamp_hicolor
>    14.85% faster in gradient_conicalOutZero_clamp_3color
>    16.72% faster in gradient_conicalOut_clamp
>    24.30% faster in gradient_conicalOut_clamp_3color
> 
> CQ_INCLUDE_TRYBOTS=skia.primary:Test-Android-Clang-Nexus7-GPU-Tegra3-arm-Release-All-Android,Test-Android-Clang-Nexus7-GPU-Tegra3-arm-Debug-All-Android
> 
> Bug: skia:
> Change-Id: I6bc1f24c9463fc9c2acbcba7bd4d55b37ade1613
> Reviewed-on: https://skia-review.googlesource.com/82161
> Reviewed-by: Greg Daniel <egdaniel@google.com>
> Commit-Queue: Yuqian Li <liyuqian@google.com>

TBR=egdaniel@google.com,fmalita@google.com,liyuqian@google.com

Change-Id: Ieb20cce12a958abb8293218b89baf3d5a2aad0a8
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:
Cq-Include-Trybots: skia.primary:Test-Android-Clang-Nexus7-GPU-Tegra3-arm-Release-All-Android, Test-Android-Clang-Nexus7-GPU-Tegra3-arm-Debug-All-Android
Reviewed-on: https://skia-review.googlesource.com/84801
Reviewed-by: Yuqian Li <liyuqian@google.com>
Commit-Queue: Yuqian Li <liyuqian@google.com>
5 files changed