Revert "implemented mustImplementGSInvocationsWithLoop workaround in sksl"

This reverts commit d5d323f45777c4766ddf4c74eedff36ee5d9bc56.

Reason for revert: Looks like this might be breaking vulkan

Original change's description:
> implemented mustImplementGSInvocationsWithLoop workaround in sksl
> 
> Bug: skia:
> Change-Id: I8434be89537a8baf9e9c5c7a643d28c03108f4ea
> Reviewed-on: https://skia-review.googlesource.com/18154
> Reviewed-by: Chris Dalton <csmartdalton@google.com>
> Commit-Queue: Ethan Nicholas <ethannicholas@google.com>

TBR=csmartdalton@google.com,ethannicholas@google.com

Change-Id: I606aad071d3c084eb7eb7ec6c1c1a3cf10479cec
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:
Reviewed-on: https://skia-review.googlesource.com/20045
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
8 files changed