Revert "Rename gl_SampleMask to sk_SampleMask"

This reverts commit 23716d42f730c62b3e198310a5cc1b324f6de4e1.

Reason for revert: red bots and GMs

Original change's description:
> Rename gl_SampleMask to sk_SampleMask
> 
> Change-Id: I3924c6f76edf310a984e4fd89478b00eeec69722
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/249931
> Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
> Commit-Queue: Chris Dalton <csmartdalton@google.com>

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

Change-Id: I74848e95972cf2c41cc28887e26214136ce79e08
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/250180
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
diff --git a/src/gpu/glsl/GrGLSLFragmentShaderBuilder.cpp b/src/gpu/glsl/GrGLSLFragmentShaderBuilder.cpp
index 7402464..85dc827 100644
--- a/src/gpu/glsl/GrGLSLFragmentShaderBuilder.cpp
+++ b/src/gpu/glsl/GrGLSLFragmentShaderBuilder.cpp
@@ -105,15 +105,15 @@
     if (!fHasModifiedSampleMask) {
         fHasModifiedSampleMask = true;
         if (ScopeFlags::kTopLevel != scopeFlags) {
-            this->codePrependf("sk_SampleMask[0] = ~0;");
+            this->codePrependf("gl_SampleMask[0] = ~0;");
         }
         if (!(ScopeFlags::kInsideLoop & scopeFlags)) {
-            this->codeAppendf("sk_SampleMask[0] = (%s);", mask);
+            this->codeAppendf("gl_SampleMask[0] = (%s);", mask);
             return;
         }
     }
 
-    this->codeAppendf("sk_SampleMask[0] &= (%s);", mask);
+    this->codeAppendf("gl_SampleMask[0] &= (%s);", mask);
 }
 
 void GrGLSLFragmentShaderBuilder::applyFnToMultisampleMask(