"makeentry" comments in Catena4410_gk_lorawan_keys.cpp are out of date

[terrillmoore]

ttnctl has evolved but the comments have not.

• update comments in Catena4410_gk_lorawan_keys.cpp and Catena4410_gk_lorawan_keys.cpp for the script that uses ttnctl

• break out the script to a file in extra/ directory.