Revert "Convert GrDitherEffect to a runtime FP"

This reverts commit 2fa843abc261d9caa16b9f64ccabbc165b1431fe.

Reason for revert: Oops, SkSL error in the ES2 path.

Original change's description:
> Convert GrDitherEffect to a runtime FP
>
> Includes a change so that we can create non-ES2 runtime effects, even
> outside of tests/tools. It's still locked to a private API, so clients
> can't access the functionality.
>
> Change-Id: Ie0643da2071bd223fccf05b35f3a7b6f7bbc4876
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/423578
> Reviewed-by: Brian Salomon <bsalomon@google.com>
> Commit-Queue: Brian Osman <brianosman@google.com>

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

Change-Id: Icff68da3cadd00868c94b84fbb39e470a7bf45d0
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/424100
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
diff --git a/src/gpu/GrProcessorUnitTest.cpp b/src/gpu/GrProcessorUnitTest.cpp
index 1779050..b4c673f 100644
--- a/src/gpu/GrProcessorUnitTest.cpp
+++ b/src/gpu/GrProcessorUnitTest.cpp
@@ -146,7 +146,7 @@
  * we verify the count is as expected.  If a new factory is added, then these numbers must be
  * manually adjusted.
  */
-static constexpr int kFPFactoryCount = 16;
+static constexpr int kFPFactoryCount = 17;
 static constexpr int kGPFactoryCount = 14;
 static constexpr int kXPFactoryCount = 4;