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.

src/lib/subs/nuke.c

@@ -77,14 +77,6 @@ nuk_prewrite(int n, void *old, void *new)
     np->nuk_own = own;
 }
 
-void
-nuk_oninit(void *ptr)
-{
-    struct nukstr *np = ptr;
-
-    np->nuk_plane = -1;
-}
-
 char *
 prnuke(struct nukstr *np)
 {