ipatests/test_ipaserver/test_install/test_installer.py: Drop tempfile import
    
    This is not needed anymore due to the removal of the DL0 test
    
    See: https://pagure.io/freeipa/issue/7669
    Signed-off-by: Thomas Woerner <twoerner@redhat.com>
    Reviewed-By: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>