vnconfig: remove -c compat

[Klemens Nanni]

OK?

Index: vnconfig.c
===================================================================
RCS file: /cvs/src/sbin/vnconfig/vnconfig.c,v
retrieving revision 1.7
diff -u -p -r1.7 vnconfig.c
--- vnconfig.c  25 Oct 2021 19:54:29 -0000      1.7
+++ vnconfig.c  16 Aug 2022 14:01:29 -0000
@@ -78,11 +78,8 @@ main(int argc, char **argv)
 
        action = VND_CONFIG;
 
-       while ((ch = getopt(argc, argv, "ckK:lo:S:t:uv")) != -1) {
+       while ((ch = getopt(argc, argv, "kK:lo:S:t:uv")) != -1) {
                switch (ch) {
-               case 'c':
-                       /* backwards compat: delete in 2020 */
-                       break;
                case 'k':
                        opt_k = 1;
                        break;