Updated test_pam_responder.py
    
    Integration tests/CI: Updated test_pam_responder.py and removed libnss3-dev and libnspr4-dev from Debian dependency list
    
     - Modified functions create_nssdb_fixture and create_nssdb_no_cert_fixture inside test_pam_responder.py file. These functions will produce the output only if environment variable USE_NSS is defined and set
     - Since CI build for Debian is using OpenSSL this improvement allowed to drop libnss3-dev and libnspr4-dev from Debian dependency list in contrib/ci/deps.sh
    
    Resolves: https://pagure.io/SSSD/sssd/issue/3914
    
    Reviewed-by: Alexey Tikhonov <atikhono@redhat.com>
    Reviewed-by: Sumit Bose <sbose@redhat.com>