strings: simplify repeat()

vlib/strings/strings.v

@@ -4,11 +4,7 @@ pub fn repeat(c byte, n int) string {
 	if n <= 0 {
 		return ''
 	}
-	//mut arr := malloc(n + 1)
-	mut arr := [byte(0)].repeat(n + 1)
-	for i := 0; i < n; i++ {
-		arr[i] = c
-	}
+	mut arr := [c].repeat(n + 1)
 	arr[n] = `\0`
 	return string(arr, n)
 }