Revert "nmap: use python infra's .withPackages"

This reverts commit 278d3050 because it
breaks zenmap:

$ zenmap
Could not import the zenmapGUI.App module: 'No module named zenmapGUI.App'.
I checked in these directories:
    /nix/store/2hiz11plgjdrk2mziwc2jcxqalqh9hii-nmap-graphical-7.12/bin
    /home/bfo/forks/nixpkgs
    /nix/store/0l4lriqf07qah8c0kh9kcyc8l5iyij16-python-2.7.12/lib/python27.zip
    /nix/store/0l4lriqf07qah8c0kh9kcyc8l5iyij16-python-2.7.12/lib/python2.7
    /nix/store/0l4lriqf07qah8c0kh9kcyc8l5iyij16-python-2.7.12/lib/python2.7/plat-linux2
    /nix/store/0l4lriqf07qah8c0kh9kcyc8l5iyij16-python-2.7.12/lib/python2.7/lib-tk
    /nix/store/0l4lriqf07qah8c0kh9kcyc8l5iyij16-python-2.7.12/lib/python2.7/lib-old
    /nix/store/0l4lriqf07qah8c0kh9kcyc8l5iyij16-python-2.7.12/lib/python2.7/lib-dynload
    /nix/store/0l4lriqf07qah8c0kh9kcyc8l5iyij16-python-2.7.12/lib/python2.7/site-packages
If you installed Zenmap in another directory, you may have to add the
modules directory to the PYTHONPATH environment variable.