Revert "Fix a bug that will not send a will message in some cases"

This reverts commit 675edf3fab850c99c87123a1b8a970d8f06aea30.

src/emqx_session.erl

@@ -963,8 +963,7 @@ ensure_expire_timer(State) ->
 
 ensure_will_delay_timer(State = #state{will_msg = #message{headers = #{'Will-Delay-Interval' := WillDelayInterval}}}) ->
     State#state{will_delay_timer = emqx_misc:start_timer(WillDelayInterval * 1000, will_delay)};
-ensure_will_delay_timer(State = #state{will_msg = WillMsg}) ->
-    send_willmsg(WillMsg),
+ensure_will_delay_timer(State) ->
     State.
 
 ensure_stats_timer(State = #state{enable_stats = true, stats_timer = undefined,