Revert "Add WCharacter support (#96)" (#99)

This reverts commit 07e65b7.

Author: TianpeiLee

cores/arduino/Arduino.h

@@ -49,14 +49,6 @@ void yield(void);
 } // extern "C"
 #endif // __cplusplus
 
-#ifdef __cplusplus
-#  include "WCharacter.h"
-#  include "WString.h"
-#  include "WMath.h"
-//#  include <Tone.h>
-#  include <HardwareSerial.h>
-#endif
-
 // Include pins variant
 #include "pins_arduino.h"