Move namePrefix="" python packages out of python-packges.nix

It doesn't make sense to build tools/applications with three different
python interpreter versions, so move them out of python modules list.

Also reverts 53ffc6e0ef395a2bd7651423d9783ad8184be1d0.
Merge pull request #794 from NixOS/python_move_nameprefix_packages

Move namePrefix="" python packages out of python-packges.nix