Remove / Replace EGI reader by https://pypi.org/project/mffpy/

[agramfort]

See EGI now offers a reference implementation to read/write EGI files we should drop our implementation in favor of the standard one.

we just need someone to do the job :)

[ViridianForge]

Thanks for opening this issue @agramfort!

Just wanted to call out that if anyone runs into any issues with the library - feel free to open an issue on it at: https://github.com/BEL-Public/mffpy - and the maintainers at @BEL-Public will be happy to give you hand.

Also - small correction: The reference spec is being provided by BELCO, which is a small company run by Drs. Tucker and Luu.