Tweak #10162 documentation a bit

changes/prop157-require

@@ -2,4 +2,4 @@
     - Clients now reject any directory authority certificates lacking
       a dir-key-crosscert element. These have been included since
       0.2.1.9-alpha, so there's no real reason for them to be optional
-      any longer. Completes proposal 157.
+      any longer. Completes proposal 157.

src/or/routerparse.c

@@ -1737,8 +1737,6 @@ authority_cert_parse_from_string(const char *s, const char **end_of_string)
     }
 
     tok = find_by_keyword(tokens, K_DIR_KEY_CROSSCERT);
-    /* XXXX Once all authorities generate cross-certified certificates,
-     * make this field mandatory. */
     if (check_signature_token(cert->cache_info.identity_digest,
                               DIGEST_LEN,
                               tok,