pg_basebackup: Correct error message

It still thought that the --xlog-method option argument could be
empty, as in a previous version of this feature.

src/bin/pg_basebackup/pg_basebackup.c

@@ -1332,7 +1332,7 @@ main(int argc, char **argv)
 				else
 				{
 					fprintf(stderr,
-							_("%s: invalid xlog-method option \"%s\", must be empty, \"fetch\", or \"stream\"\n"),
+							_("%s: invalid xlog-method option \"%s\", must be \"fetch\" or \"stream\"\n"),
 							progname, optarg);
 					exit(1);
 				}