Update attend-event-ajax.rst

getRequest() comes up as deprecated for 2.4.
Update attend-event-ajax.rst

Reverted back original getRequest and added the preferred method for type hinting on attendAction(Request $request, $id) and unattendAction (Request $request, $id).
Updating controller to use the newly-type-hinted $request argument

This removes the deprecated getRequest call
Adding ERRATA about these changes
Merge pull request #13 from knpuniversity/keefekwan-patch-3

Remove deprecated getRequest()