remove the unimplemented lv_ll_swap

src/lv_misc/lv_ll.c

@@ -335,14 +335,6 @@ uint32_t lv_ll_get_len(const lv_ll_t * ll_p)
     return len;
 }
 
-void lv_ll_swap(lv_ll_t * ll_p, void * n1_p, void * n2_p)
-{
-    (void)(ll_p);
-    (void)(n1_p);
-    (void)(n2_p);
-    /*TODO*/
-}
-
 /**
  * Move a nodw before an other node in the same linked list
  * @param ll_p pointer to a linked list