linked-list: Remove unused replace() method

Its functionality can be replicated by calling insert_before() followed
by remove_at().  Not the other way around, though, because remove_at()
changes the enumerator position.

src/libstrongswan/collections/linked_list.h

@@ -117,16 +117,6 @@ struct linked_list_t {
 	void (*insert_before)(linked_list_t *this, enumerator_t *enumerator,
 						  void *item);
 
-	/**
-	 * Replaces the item the enumerator currently points to with the given item.
-	 *
-	 * @param enumerator	enumerator with position
-	 * @param item			item value to replace current item with
-	 * @return				current item or NULL if the enumerator is at an
-	 *						invalid position
-	 */
-	void *(*replace)(linked_list_t *this, enumerator_t *enumerator, void *item);
-
 	/**
 	 * Remove an item from the list where the enumerator points to.
 	 *