Revert "Allow FPs to elevate default precision for the entire fragment program"

Revert "Allow FPs to elevate default precision for the entire fragment program"

This reverts commit 92d7ccafdf896cf19764e025873d13315a76842d.

Reason for revert: Vulkan errors.

Original change's description:
> Allow FPs to elevate default precision for the entire fragment program
>
> Currently, GrConfigConversionEffect is able to round-trip on many mobile
> GPUs because it uses highp for all intermediate variables (including the
> texture fetch result). Separating the texture sample into a different
> processor breaks that.
>
> This is a blunt instrument, not to be used lightly.
>
> Bug: skia:
> Change-Id: I2ab365e3da79628069e2eb727c43c2bf45bfd789
> Reviewed-on: https://skia-review.googlesource.com/10162
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Brian Osman <brianosman@google.com>
>

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

Change-Id: Iee5bb409f86a9cabecc76bd1273a5b3cef6af179
Reviewed-on: https://skia-review.googlesource.com/10967
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>