Remove a superfluous comment.
diff --git a/src/arena.c b/src/arena.c
index 1ceb59f..ec4315a 100644
--- a/src/arena.c
+++ b/src/arena.c
@@ -3049,7 +3049,6 @@
 	/* Calls with non-zero extra had to clamp extra. */
 	assert(extra == 0 || size + extra <= HUGE_MAXCLASS);
 
-	/* Prevent exceeding PTRDIFF_MAX. */
 	if (unlikely(size > HUGE_MAXCLASS))
 		return (true);