Minor cppcheck fixes (#5689)

* In graphics/Screen.cpp, a copy/paste error to do with hearts
* In mesh/http/ContentHandler.cpp, an unused variable
* in mqtt/MQTT.cpp, remove unneded logic " '!A || (A && B)' is equivalent to '!A || B'"

src/mesh/http/ContentHandler.cpp

@@ -725,7 +725,6 @@ void handleNodes(HTTPRequest *req, HTTPResponse *res)
                 node["position"] = new JSONValue(position);
             }
 
-            JSONObject user;
             node["long_name"] = new JSONValue(tempNodeInfo->user.long_name);
             node["short_name"] = new JSONValue(tempNodeInfo->user.short_name);
             char macStr[18];