chore(syncer): fix code style issues

Co-Authored-By: Zaiming (Stone) Shi <zmstone@gmail.com>

apps/emqx/src/emqx_router_syncer.erl

@@ -78,7 +78,7 @@ push(Action, Topic, Dest, Opts) ->
     Worker = gproc_pool:pick_worker(?POOL, Topic),
     Prio = designate_prio(Action, Opts),
     Context = mk_push_context(Opts),
-    Worker ! ?PUSH(Prio, {Action, Topic, Dest, Context}),
+    _ = erlang:send(Worker, ?PUSH(Prio, {Action, Topic, Dest, Context})),
     case Context of
         {MRef, _} ->
             MRef;
@@ -148,7 +148,7 @@ run_batch_loop(Incoming, State = #{stash := Stash0}) ->
     ok = send_replies(Errors, Batch),
     NState = State#{stash := Stash3},
     %% TODO: postpone if only ?PRIO_BG operations left?
-    case stash_empty(Stash3) of
+    case is_stash_empty(Stash3) of
         true ->
             NState;
         false ->
@@ -209,7 +209,8 @@ send_replies(Errors, Batch) ->
 replyctx_send(_Result, []) ->
     noreply;
 replyctx_send(Result, {MRef, Pid}) ->
-    Pid ! {MRef, Result}.
+    _ = erlang:send(Pid, {MRef, Result}),
+    ok.
 
 %%
 
@@ -221,7 +222,7 @@ run_batch(Batch) ->
 stash_new() ->
     #{}.
 
-stash_empty(Stash) ->
+is_stash_empty(Stash) ->
     maps:size(Stash) =:= 0.
 
 stash_drain(Stash) ->