Changes are:
- Remove the LED_Pxxx definitions from pins.csv, now that the LED class is
gone.
- Remove the '-' lines.
- Add default lines for USB and SWCLK, SWDIO.
Instead of being hard-coded, and then it works for all MCUs.
That fits except for a Sparkfun SAMD51 Thing Plus (known) bug, which uses
192k - 4 as magic address. Therefore, that address is set as well to avoid
a problem when this bug is fixed by Sparkfun.