Remove FAM/gamin file monitor
Gamin has last been released in 2007, and it's dead upstream. Linux distributions may still ship it, but we definitely want people to use inotify on Linux.
*BSDs have the kqueue monitor, so they don't need gamin at all.
The only place where FAM can possibly still be used is some random commercial UNIX that we don't even have under CI.
I think it's time to call it.