remove mmtf in 3.0

[orbeckst]

Remove all mmtf-handling code for 3.0.

• MMTF is no longer supported by PDB (see fetch_mmtf no longer works #4634 )
• the mmtf-python license is incompatible with our target license LGPLv2.1+ (see https://www.mdanalysis.org/2023/09/22/licensing-update/#why-the-interim-gpl-v3-and-lgpl-v3-package-licenses-the-issue-with-apache-20 )

[talagayev]

@orbeckst so if I understand correct the PR for this would be the complete removal of all of the code involved with mmtf, such as MMTF.py and MMTFParser.py and other, then the removal of pytests and data files for MMTF, the documentation and also the removal of mmtf-python as an dependency?

[IAlibay]

@talagayev if it's ok, I would like to do this when we're ready to - in the sense that I would want to do this along switching things fully up lgplv2.1+ since we'll be touching the packaging.

[IAlibay]

I'm going to do one of those rare self assignments here, someone give us a shout if you feel I shouldn't be.

[talagayev]

@talagayev if it's ok, I would like to do this when we're ready to - in the sense that I would want to do this along switching things fully up lgplv2.1+ since we'll be touching the packaging.

Hey @IAlibay yes of course :) makes sense, since if the dependency of mmtf-python you need to adjust conda-forge etc. to remove it from there.

If there is anything I can do to help you I would be glad to help though :)