TESTS: remove NSS test databases
    
    NSS databases with the certificates from the test CA will be
    automatically generated. The static databases are not needed anymore.
    
    Related to https://pagure.io/SSSD/sssd/issue/3436
    
    Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>
    (cherry picked from commit cbcb2dab1ba06c65d64910b733f4480b5cf5d090
    with fixes)