Reason for revert:
Co-centered sample locations are not needed to do stencil clip with mixed samples.
Original issue's description:
> Fix mixed samples stencil clip
>
> Fixes rendering bugs and nondeterminism in gm.
>
> Before, mixed samples stencil clip would try to infer whether the draw
> wanted co-centered sample locations from within GrGLGpu, which caused
> various errors. This change reworks it so the draw itself can request
> the co-centered sample locations when it knows it will need them.
>
> Also reduces framebuffer binds by moving the code that enables
> GL_FRAMEBUFFER_PROGRAMMABLE_SAMPLE_LOCATIONS into flushRenderTarget.
>
> Committed: https://skia.googlesource.com/skia/+/14184d5567b58085b6d8a6375796d405056f7f73TBR=bsalomon@google.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
Review URL: https://codereview.chromium.org/1407063011
d472792a72