Revert "converted GrCircleBlurFragmentProcessor to sksl"

This reverts commit 9b80ffc77b8000b493eb1226dc6ec21f1e99edfc.

Reason for revert: breaking ANGLE and Android Vulkan GMs

Original change's description:
> converted GrCircleBlurFragmentProcessor to sksl
> 
> Bug: skia:
> Change-Id: I1b70ba2003c9e9de2b5b9acadaf25c9ed59b1198
> Reviewed-on: https://skia-review.googlesource.com/21727
> Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
> Reviewed-by: Brian Salomon <bsalomon@google.com>

TBR=bsalomon@google.com,ethannicholas@google.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: skia:
Change-Id: Ia313013b4354b34fa5a02bdb16d007a462c5ca94
Reviewed-on: https://skia-review.googlesource.com/22028
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
12 files changed