remove unused import from nsa.py and clarify module use
remove unused import from nsa.py and clarify module use

jeroenh/OpenNSA,jeroenh/OpenNSA,jab1982/opennsa,NORDUnet/opennsa,jab1982/opennsa,jeroenh/OpenNSA,NORDUnet/opennsa,NORDUnet/opennsa