remove useless test ..

core.js

@@ -406,12 +406,8 @@
             // Prevent a memory leak in IE.
             try {
                 // Check if delete is supported
-                if (delete({})) {
                 delete(obj[type + listener]);
                 delete(obj['__e' + type + listener]);
-                } else {
-                    throw "delete";
-                };
             } catch(e) {
                 obj[type + listener] = null;
                 obj['__e' + type + listener] = null;