fix: remove unused boolean ssl field

common/transport/mqtt/src/main/java/org/thingsboard/server/transport/mqtt/MqttTransportHandler.java

@@ -150,7 +150,6 @@ public class MqttTransportHandler extends ChannelInboundHandlerAdapter implement
     protected final MqttTransportContext context;
     private final TransportService transportService;
     private final SchedulerComponent scheduler;
-    private final boolean ssl;
     private volatile SslHandler sslHandler;
     private final ConcurrentMap<MqttTopicMatcher, Integer> mqttQoSMap;
 
@@ -173,7 +172,6 @@ public class MqttTransportHandler extends ChannelInboundHandlerAdapter implement
         this.context = context;
         this.transportService = context.getTransportService();
         this.scheduler = context.getScheduler();
-        this.ssl = sslHandler != null;
         this.sslHandler = sslHandler;
         this.mqttQoSMap = new ConcurrentHashMap<>();
         this.deviceSessionCtx = new DeviceSessionCtx(sessionId, mqttQoSMap, context);