Move pln_oninit(), lnd_oninit(), nuk_oninit() to filetable.c

Move pln_oninit(), lnd_oninit(), nuk_oninit() to filetable.c

They set up invariants, and thus should be always active, not just in
the server.  Since ef_blank() isn't used for these files outside the
server right now, this isn't a bug fix, just cleanup.