py3 spec: remove python2 dependencies from freeipa-server
    
    When building the package with for python3, use only python3
    dependencies. Changed:
      python -> python2 / python3
      python-gssapi -> python2-gssapi / python3-gssapi
      python-ldap -> python-ldap / python3-pyldap
      systemd-python -> python2-systemd / python3-systemd
    
    Fixes: https://pagure.io/freeipa/issue/7208
    Signed-off-by: Tomas Krizek <tkrizek@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>