Delete README.md

The info in it is now moved to the firmware-pinoccio repository, so no
longer needed here.
Remove __PROG_TYPES_COMPAT__ workaround

In Arduino 1.5.6, https://github.com/arduino/Arduino/pull/1695 got
merged which removes the need for this workaround.
Merge the 128rfa1 and 256rfr2 board.txt entries

Now, there is just a single "Pinoccio Scout" board in the Arduino IDE.
However, there is now also a "Processor" submenu, that allows choosing
between the two boards.