selftests/user_events: Clear the events after perf self-test

When the self test is completed, perf self-test left the user events not to
be cleared. Clear the events by unregister and delete the event.

Link: https://lkml.kernel.org/r/20230606062027.1008398-4-sunliming@kylinos.cn



Acked-by: Beau Belgrave <beaub@linux.microsoft.com>
Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: sunliming <sunliming@kylinos.cn>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>