Fixed-width integer type aliases are leaked from `USBAPI.h`

[inicula]

It seems inappropriate that u8, u16, and u32 are leaked from USBAPI.h, which in turn is included in Arduino.h, and thus polluting the global namespace:

ArduinoCore-avr/cores/arduino/USBAPI.h

Lines 29 to 31 in 42fa4a1

	typedef unsigned char u8;
	typedef unsigned short u16;
	typedef unsigned long u32;

If you try to define u16 yourself as using u16 = uint16_t; while including Arduino.h, you'll get a compilation error because this alias conflicts with the one from USBAPI.h.

Is this behavior intended?

[matthijskooijman]

Sounds wrong to me, I'd be in favor of removing them. Especially since (at first glance) it seems the header file does not actually use these types at all either.