tests/acceptance: Remove shebang header

Patch created mechanically by running:

  $ chmod 644 $(git grep -lF '#!/usr/bin/env python' \
      | xargs grep -L 'if __name__.*__main__')
  $ sed -i "/^#\!\/usr\/bin\/\(env\ \)\?python.\?$/d" \
      $(git grep -lF '#!/usr/bin/env python' \
      | xargs grep -L 'if __name__.*__main__')

Reported-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Suggested-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Wainer dos Santos Moschetta <wainersm@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20200130163232.10446-8-philmd@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>