resources-test: Don't send invalid event

Even if nothing receives the even, the arguments still need to be valid.
The test is sending out event 0 from the wl_display interface, which is
the error event.  This requires arg 0 to be a valid object and arg 2 to
be a non-null string.  The test just leaves that undefined, causing
intermittent test failures.

As it is, the resource destroy test doesn't need to send an event to
validate the various resource destroy hooks, so we can just remove the
call to wl_resource_post_event() alltogether.

Thanks to Matt Turner <mattst88@gmail.com> for pointing out the failure.