avoid use of mne_surf2bem

[agramfort]

we should remove the use of mne C tool mne_surf2bem in mne-python.

[larsoner]

This would require translating mne_surf2bem, right? It should be pretty simple, I think.

[agramfort]

yes it's nothing. We have everything already. Just 2 hours to find :(

[larsoner]

Actually it looks like we don't need to add anything, just modify calls. We already have write_bem_surfaces(fname, surfs), so we should just need to make the list of dict surfs properly.

[agramfort]

so 20 mins not 2 hours? :)