Revert "Add support for image load to SkSL"

This reverts commit bd85a105ba7b3ee2008d20fb9281bfb47325ad0e.

Reason for revert: Needing to revert a dependent CL

Original change's description:
> Add support for image load to SkSL
> 
> GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4865
> 
> Change-Id: I4647e6b255946ced2b1b8cb05e62f0f5a8ad28b6
> Reviewed-on: https://skia-review.googlesource.com/4865
> Commit-Queue: Brian Salomon <bsalomon@google.com>
> Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
> 

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

Change-Id: I45932a53c606aadd645ee2b8264f08ad63429939
Reviewed-on: https://skia-review.googlesource.com/4892
Commit-Queue: Stan Iliev <stani@google.com>
Reviewed-by: Stan Iliev <stani@google.com>