build: Remove python 2 build
    
    Python 2 is EOL since Jan 2020, but we kept the option to build for
    python2. Remove this option so we can remove the python 2 hacks from the
    sanlock C extension module.
    
    Users that want python 2 support should use sanlock <= 3.8.2.
    
    Signed-off-by: Nir Soffer <nsoffer@redhat.com>