unpack-objects: remove stale and confusing comment

The very initial version of unpack-objects.c::unpack_all() used
to unpack from the end of the pack, but since end of June last
year it was changed to stream from the front and the comment
does not reflect the reality anymore.

Signed-off-by: Junio C Hamano <junkio@cox.net>

unpack-objects.c

@@ -241,11 +241,6 @@ static void unpack_one(unsigned nr, unsigned total)
 	}
 }
 
-/*
- * We unpack from the end, older files first. Now, usually
- * there are deltas etc, so we'll not actually write the
- * objects in that order, but we might as well try..
- */
 static void unpack_all(void)
 {
 	int i;