py: Implement DELETE_SUBSCR bytecode; implement mp_obj_dict_delete.
diff --git a/py/vm.c b/py/vm.c
index 6186bbc..167de1d 100644
--- a/py/vm.c
+++ b/py/vm.c
@@ -324,6 +324,11 @@
                         mp_delete_name(qst);
                         break;
 
+                    case MP_BC_DELETE_SUBSCR:
+                        mp_delete_subscr(sp[-1], sp[0]);
+                        sp -= 3;
+                        break;
+
                     case MP_BC_DUP_TOP:
                         obj1 = TOP();
                         PUSH(obj1);