Make list clear nulls faster (#80869)

The old version makes a new list of n null values, and removes it from
the given list.

for larger lists, this newer 515 version should be faster and lead to
less list churn.


![image](https://github.com/tgstation/tgstation/assets/7069733/9c23cc8b-06c4-4a54-99b4-2c44608cf434)

code/__HELPERS/_lists.dm

@@ -403,10 +403,8 @@
  * Returns TRUE if the list had nulls, FALSE otherwise
 **/
 /proc/list_clear_nulls(list/list_to_clear)
-	var/start_len = list_to_clear.len
-	var/list/new_list = new(start_len)
-	list_to_clear -= new_list
-	return list_to_clear.len < start_len
+	return (list_to_clear.RemoveAll(null) > 0)
+	
 
 /**
  * Removes any empty weakrefs from the list