use $.detachArrayBuffer API instead of throwing (#795)

harness/detachArrayBuffer.js

 function $DETACHBUFFER(buffer) {
-  throw new Test262Error("No method available to detach an ArrayBuffer");
+  if (!$ || typeof $.detachArrayBuffer !== "function") {
+    throw new Test262Error("No method available to detach an ArrayBuffer");
+  }
+  $.detachArrayBuffer(buffer);
 }