Revert "impl. _clamp_8888 shaders using general mechanism"

This reverts commit dfa1de9180e4b26b08aa60d27472b6548bb0967c.

Reason for revert: 1 Google3 Scuba diff.  :/

Original change's description:
> impl. _clamp_8888 shaders using general mechanism
> 
> This should result in roughly the same binary at
> the same speed but with less duplication of code.
> 
> The idea is that we take all the runtime configurable
> fields and make it clear to the compiler that they're
> actually constants, and it propagates them through.
> 
> Order of operations does change slightly up in the float
> code and some operations become FMAs so there are tiny
> invisible diffs when we don't hit lowp.
> 
> Cq-Include-Trybots: luci.chromium.try:linux-blink-rel
> Change-Id: Ic9d44207bcad39d0cf96c0b55bd65fb61997194f
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/249054
> Reviewed-by: Mike Reed <reed@google.com>
> Commit-Queue: Mike Klein <mtklein@google.com>

TBR=mtklein@google.com,reed@google.com

Change-Id: Ic549e8c6488dc6db1d71e34f5e06fcdf9410c8b6
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Cq-Include-Trybots: luci.chromium.try:linux-blink-rel
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/249279
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
1 file changed