[turbofan] Remove unused BuildLoadGlobalProxy from AstGraphBuilder.

R=jarin@chromium.org

Review URL: https://codereview.chromium.org/1413783010

Cr-Commit-Position: refs/heads/master@{#31880}

src/compiler/ast-graph-builder.cc

@@ -3653,14 +3653,6 @@ Node* AstGraphBuilder::BuildLoadNativeContextField(int index) {
 }
 
 
-Node* AstGraphBuilder::BuildLoadGlobalProxy() {
-  Node* global = BuildLoadGlobalObject();
-  Node* proxy =
-      BuildLoadObjectField(global, JSGlobalObject::kGlobalProxyOffset);
-  return proxy;
-}
-
-
 Node* AstGraphBuilder::BuildLoadFeedbackVector() {
   if (!feedback_vector_.is_set()) {
     Node* closure = GetFunctionClosure();

src/compiler/ast-graph-builder.h

@@ -301,7 +301,6 @@ class AstGraphBuilder : public AstVisitor {
   // Builders for accessing the function context.
   Node* BuildLoadGlobalObject();
   Node* BuildLoadNativeContextField(int index);
-  Node* BuildLoadGlobalProxy();
   Node* BuildLoadFeedbackVector();
 
   // Builder for accessing a (potentially immutable) object field.