rfc822: Update rfc822 module to use testdepends

Several modules were only listed as dependencies because they were used in
the testcases.  That in turn gave some bogus incompatible license warnings
which we partially suppressed from _info.  Now that ccanlint supports
testdepends, use that to clean it up.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

ccan/rfc822/_info

@@ -33,9 +33,6 @@
  *
  * License: LGPL (v2.1 or any later version)
  *
- * Ccanlint:
- *	// The failtest module is only used for tests: ccanlint is overzealous
- *	license_depends_compat FAIL
  */
 int main(int argc, char *argv[])
 {
@@ -44,15 +41,19 @@ int main(int argc, char *argv[])
 		return 1;
 
 	if (strcmp(argv[1], "depends") == 0) {
-		printf("ccan/array_size\n");
 		printf("ccan/talloc\n");
 		printf("ccan/list\n");
-		printf("ccan/foreach\n");
-		printf("ccan/failtest\n");
 		printf("ccan/str\n");
 		printf("ccan/bytestring\n");
 		return 0;
 	}
 
+	if (strcmp(argv[1], "testdepends") == 0) {
+		printf("ccan/failtest\n");
+		printf("ccan/foreach\n");
+		printf("ccan/array_size\n");
+		return 0;
+	}
+
 	return 1;
 }