After this test had been fixed for freebsd the debug build was broken because
we can't call evthread_set_lock_callbacks() when something already initialized,
and we can't call event_base_free() (in kqueue case) when it is initialized,
because of "held_by", but this only playing role during freeing lock profiler
so reset lock callbacks there before and this will fix both.
Fixes: 79f9ace4ae8a259a5cf1b4ff3869078b60ff16a1 ("test: fix
bufferevent/bufferevent_pair_release_lock for freebsd")
P.S. after this patch 'make verify' finishes without errors on freebsd.