Only use libevent2

Remove libevent as libevent2 is providing a good compatibility interface as well
as providing better performances.
Remove custom patches from libevent2 and install libevent2 the regular way
Mark ports abusing private fields of the libevent1 API as broken
Import a patch from fedora to have honeyd working with libevent2
Remove most of the patches necessary to find the custom installation we used to
have for libevent2

With hat: portmgr