remove extraneous includes from WProgram.h

since 'Serial' is faked as USB Serial, only usb_serial.h is needed here
to "trick" dependent libraries. including the other usb headers there
just adds bloat to an already overbloated header (ala typical
Arduino-style includes)

include/core/Arduino.h

 #ifndef Arduino_h
 #define Arduino_h
 
-#include "core/WProgram.h"
-#include "core/pins_arduino.h"
+#include "./WProgram.h"
+#include "./pins_arduino.h"
 
 #endif

include/core/WProgram.h

 
 #include "core/avr_emulation.h"
 #include "core/usb_serial.h"
-#include "core/usb_seremu.h"
-#include "core/usb_keyboard.h"
-#include "core/usb_mouse.h"
-#include "core/usb_joystick.h"
-#include "core/usb_midi.h"
-#include "core/usb_rawhid.h"
-#include "core/usb_flightsim.h"
-//#include "core/usb_mtp.h"
-#include "core/usb_audio.h"
-#include "core/usb_touch.h"
-//#include "core/usb_undef.h" // do not allow usb_desc.h stuff to leak to user programs
 
 #include "core/WCharacter.h"
 #include "core/WString.h"
-#include "core/elapsedMillis.h"
-#include "core/IntervalTimer.h"
 
 uint16_t makeWord(uint16_t w);
 uint16_t makeWord(byte h, byte l);

src/core/Tone.cpp

  */
 
 #include <core/Arduino.h>
+#include <core/IntervalTimer.h>
 
 // IntervalTimer based tone.  This allows tone() to share the timers with other
 // libraries, rather than permanently hogging one PIT timer even for projects

src/core/usb_inst.cpp

 
 #include <core/Arduino.h>
 #include "core/usb_desc.h"
+#include "core/usb_serial.h"
 
 #if F_CPU >= 20000000
 

src/core/yield.cpp

 
 #include <core/Arduino.h>
 #include "core/EventResponder.h"
+#include "core/usb_serial.h"
 
 #ifdef USB_TRIPLE_SERIAL
 uint8_t yield_active_check_flags = YIELD_CHECK_USB_SERIAL | YIELD_CHECK_USB_SERIALUSB1 | YIELD_CHECK_USB_SERIALUSB2; // default to check USB.