AMQ-9743: Fixes Web Console column sorting. (#1479)

Fixes an issue registering window.onload JS events, also fixes a call to
prettyPrint() with the wrong callback.

Author: sergio-d-lemos

activemq-web-console/src/main/webapp/js/head.js

@@ -14,7 +14,4 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-
-window.onload = function () {
-    addEvent(window, 'load', prettyPrint)
-}
+addEvent(window, 'load', (_event) => prettyPrint());