Change struct empfile callback onresize() to return void

ef_open() handles onresize() failing incorrectly.  Instead of fixing
that, drop the failure mode.  It's not really used: unit_onresize()
fails only when used incorrectly.  It isn't.  If it ever is, ignoring
the failure is safe.

src/lib/subs/fileinit.c

@@ -44,7 +44,7 @@ struct fileinit {
     void (*oninit)(void *);
     void (*postread)(int, void *);
     void (*prewrite)(int, void *, void *);
-    int (*onresize)(int);
+    void (*onresize)(int);
 };
 
 static struct fileinit fileinit[] = {