Revert "Switch runtime SkSL to always sample at explicit coords"

This reverts commit b1e9971eb7126d29468c42d6fa74fb8a3cfca5bd.

Reason for revert: crbug_905548 GM drawing incorrect
before: https://gold.skia.org/img/images/32964364a8ac12af5a68bf95c24fb90c.png
after : https://gold.skia.org/img/images/0918b58c93c770c20cf475c37a70b528.png

Original change's description:
> Switch runtime SkSL to always sample at explicit coords
> 
> Change-Id: I4647d0f4a098acf399e1add1d87ca0752d0fdf90
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/266381
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Brian Osman <brianosman@google.com>

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

Change-Id: I0fb892148a424d5928878a49e3ccd5bfb9485b23
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/266840
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
6 files changed