Improve getpinnmap_thisboard.cpp error handling #212
Description
It's an error to call Arduino_LMIC::GetPinmap_ThisBoard() if there's no way for it to figure out the pinmap for this board. However, it's not an error to compile a library if you don't intend to use this API. As of #204, we no longer emit a warning at compile time, but we should not emit a compile-time message, and instead we should print a runtime debug message if this routine is called and can't find the pin map.