Revert "Make blur utils take GrTextureProxies"

This reverts commit d0dc05b98b71af43b44f13beba1292db52b75539.

Reason for revert: assertion failure on N7

Original change's description:
> Make blur utils take GrTextureProxies
> 
> Change-Id: I1c5054de6d9827eece2f73c4c78818b4db0bc611
> Reviewed-on: https://skia-review.googlesource.com/7738
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Robert Phillips <robertphillips@google.com>
> 

TBR=bsalomon@google.com,robertphillips@google.com,reviews@skia.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Change-Id: I82d9385e23279db4c7a6757f1224e603e231354c
Reviewed-on: https://skia-review.googlesource.com/7744
Commit-Queue: Robert Phillips <robertphillips@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
7 files changed