Fix compiler warning symbol __AVR redefined.

Firmware/uni_avr_rpi.h

@@ -1,5 +1,4 @@
 // unification for AVR and RPI
-#define __AVR
 
 #ifdef __AVR
 	//#include "Arduino.h"
@@ -29,3 +28,4 @@
 	void print(int v) { printf("%d", v); }
 	void print(float v) { printf("%f", v); }
 #endif //RC522_RPI
+