change failsafe wstring (char16) to string (char)

src/drone_controls/src/PositionChanger.cpp

@@ -148,7 +148,7 @@ public:
      * 
      * @param message the message indicating the cause of the failsafe
      */
-    void enable_failsafe(std::__cxx11::basic_string<char16_t> message)
+    void enable_failsafe(std::string message)
     {
         this->failsafe_enabled = true;
         this->failsafe_request->message = message;

src/drone_services/msg/FailsafeMsg.msg

@@ -1,2 +1,2 @@
 bool enabled
-wstring msg
+string msg