Replace usage of #!/usr/bin/env python3 with #!/usr/bin/python3
    
    Only three remaining scripts used this form, two of which are
    for developers only and not shipped.
    
    The shebang in ipa-ccache-sweeper will be converted to
    "#!$(PYTHON) -I" in the build process.
    
    Fixes: https://pagure.io/freeipa/issue/8941
    
    Signed-off-by: Rob Crittenden <rcritten@redhat.com>
    Reviewed-By: Rafael Guterres Jeffman <rjeffman@redhat.com>