ArduSub: remove Log_Write_Performance which is not called anywhere

ArduSub/Log.cpp

@@ -346,7 +346,6 @@ void Sub::log_init()
 #else // LOGGING_ENABLED
 
 void Sub::Log_Write_Control_Tuning() {}
-void Sub::Log_Write_Performance() {}
 void Sub::Log_Write_Attitude(void) {}
 void Sub::Log_Write_MotBatt() {}
 void Sub::Log_Write_Data(LogDataID id, int32_t value) {}

ArduSub/Sub.h

@@ -428,7 +428,6 @@ private:
     void rpm_update();
 #endif
     void Log_Write_Control_Tuning();
-    void Log_Write_Performance();
     void Log_Write_Attitude();
     void Log_Write_MotBatt();
     void Log_Write_Data(LogDataID id, int32_t value);