drop unused assignment based on reduce_vars (#2709)

lib/scope.js

@@ -151,7 +151,7 @@ AST_Toplevel.DEFMETHOD("figure_out_scope", function(options){
             node.references = [];
         }
         if (node instanceof AST_SymbolLambda) {
-            defun.def_function(node);
+            defun.def_function(node, defun);
         }
         else if (node instanceof AST_SymbolDefun) {
             // Careful here, the scope where this should be defined is
@@ -318,6 +318,9 @@ AST_Scope.DEFMETHOD("def_variable", function(symbol, init){
     var def = this.variables.get(symbol.name);
     if (def) {
         def.orig.push(symbol);
+        if (def.init && (def.scope !== symbol.scope || def.init instanceof AST_Function)) {
+            def.init = init;
+        }
     } else {
         def = new SymbolDef(this, symbol, init);
         this.variables.set(symbol.name, def);