GCC: fix format_is_utf8.c:36:9: warning: variable ‘j’ set but not used [-Wunused-but-set-variable]

FossilOrigin-Name: b8df4fd31ebce957b6ef1c5101447df3439a1a90c0aa33aefe30a220107f6154

src/cw/format_is_utf8.c

@@ -33,11 +33,9 @@
 int format_is_utf8(unsigned char *str, size_t len)
 {
 	size_t i = 0;
-	size_t j = 0;
 	size_t bytes = 0;
 
 	while (i < len) {
-		j = i;
 		if (str[i] < 0x20) {
 			return 0;
 		}