add Binary node cleanup

src/babel/transformation/transformers/internal/cleanup.js

@@ -13,3 +13,18 @@ export var ExpressionStatement = {
     if (!node.expression) this.remove();
   }
 };
+
+export var Binary = {
+  exit(node) {
+    var right = node.right;
+    var left  = node.left;
+
+    if (!left && !right) {
+      this.remove();
+    } else if (!left) {
+      return right;
+    } else if (!right) {
+      return left;
+    }
+  }
+};