Revert of added support for push_constant layout

src/sksl/ir/SkSLLayout.h

Index: src/sksl/ir/SkSLLayout.h
diff --git a/src/sksl/ir/SkSLLayout.h b/src/sksl/ir/SkSLLayout.h
index dfa396758b584741049c46281ee1ebc236789237..24087d06121a817c45923235ade277b8649d7c54 100644
--- a/src/sksl/ir/SkSLLayout.h
+++ b/src/sksl/ir/SkSLLayout.h
@@ -24,11 +24,10 @@
     , fBuiltin(layout.fBuiltin)
     , fOriginUpperLeft(layout.fOriginUpperLeft)
     , fOverrideCoverage(layout.fOverrideCoverage)
-    , fBlendSupportAllEquations(layout.fBlendSupportAllEquations)
-    , fPushConstant(layout.fPushConstant) {}
+    , fBlendSupportAllEquations(layout.fBlendSupportAllEquations) {}
 
     Layout(int location, int binding, int index, int set, int builtin, bool originUpperLeft,
-           bool overrideCoverage, bool blendSupportAllEquations, bool pushconstant)
+           bool overrideCoverage, bool blendSupportAllEquations)
     : fLocation(location)
     , fBinding(binding)
     , fIndex(index)
@@ -36,19 +35,7 @@
     , fBuiltin(builtin)
     , fOriginUpperLeft(originUpperLeft)
     , fOverrideCoverage(overrideCoverage)
-    , fBlendSupportAllEquations(blendSupportAllEquations)
-    , fPushConstant(pushconstant) {}
-
-    Layout() 
-    : fLocation(-1)
-    , fBinding(-1)
-    , fIndex(-1)
-    , fSet(-1)
-    , fBuiltin(-1)
-    , fOriginUpperLeft(false)
-    , fOverrideCoverage(false)
-    , fBlendSupportAllEquations(false)
-    , fPushConstant(false) {}
+    , fBlendSupportAllEquations(blendSupportAllEquations) {}
 
     std::string description() const {
         std::string result;
@@ -85,10 +72,6 @@
             result += separator + "blend_support_all_equations";
             separator = ", ";
         }
-        if (fPushConstant) {
-            result += separator + "push_constant";
-            separator = ", ";
-        }
         if (result.length() > 0) {
             result = "layout (" + result + ")";
         }
@@ -110,16 +93,16 @@
         return !(*this == other);
     }
 
+    // everything but builtin is in the GLSL spec; builtin comes from SPIR-V and identifies which
+    // particular builtin value this object represents.
     int fLocation;
     int fBinding;
     int fIndex;
     int fSet;
     int fBuiltin;
-    int fOffset;
     bool fOriginUpperLeft;
     bool fOverrideCoverage;
     bool fBlendSupportAllEquations;
-    bool fPushConstant;
 };
 
 } // namespace