Revert "added GrSkSLFP and converted DitherEffect to use it"

This reverts commit dfbfc738a9edfff7a9804253175e380c230f3d21.

Reason for revert: Seems to be breaking DDL/ASAN bots

Original change's description:
> added GrSkSLFP and converted DitherEffect to use it
>
> Bug: skia:
> Change-Id: I84b71165eab1712355f3c7669cee2d33d259f3df
> Reviewed-on: https://skia-review.googlesource.com/124504
> Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
> Reviewed-by: Brian Salomon <bsalomon@google.com>

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

Change-Id: Ic4c3978aaba0391f2f8bb1316a456e3821a3a2f2
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: skia:
Reviewed-on: https://skia-review.googlesource.com/135700
Commit-Queue: Kevin Lubick <kjlubick@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
diff --git a/src/sksl/SkSLMain.cpp b/src/sksl/SkSLMain.cpp
index 3da90df..8ba0933 100644
--- a/src/sksl/SkSLMain.cpp
+++ b/src/sksl/SkSLMain.cpp
@@ -45,10 +45,8 @@
         kind = SkSL::Program::kGeometry_Kind;
     } else if (input.endsWith(".fp")) {
         kind = SkSL::Program::kFragmentProcessor_Kind;
-    } else if (input.endsWith(".stage")) {
-        kind = SkSL::Program::kPipelineStage_Kind;
     } else {
-        printf("input filename must end in '.vert', '.frag', '.geom', '.fp', or '.stage'\n");
+        printf("input filename must end in '.vert', '.frag', '.geom', or '.fp'\n");
         exit(1);
     }