Remove unused Zone argument from InitializeAstVisitor

src/ast-expression-visitor.cc

Index: src/ast-expression-visitor.cc
diff --git a/src/ast-expression-visitor.cc b/src/ast-expression-visitor.cc
index 4a4bc6068597fa728ea17fa6a4d3e9dc80a662ec..d534d1f0f036c1210175cd7f7b89505c7016b860 100644
--- a/src/ast-expression-visitor.cc
+++ b/src/ast-expression-visitor.cc
@@ -32,10 +32,10 @@ namespace internal {
   } while (false)
 
 
-AstExpressionVisitor::AstExpressionVisitor(Isolate* isolate, Zone* zone,
+AstExpressionVisitor::AstExpressionVisitor(Isolate* isolate,
                                            FunctionLiteral* root)
     : root_(root), depth_(0) {
-  InitializeAstVisitor(isolate, zone);
+  InitializeAstVisitor(isolate);
 }