Remove documentation of old module groups

[elstoc]

Review and tidy-up the module groups documentation (as mentioned in #652). Remove information about config migration and perhaps limit documentation to just a cursory overview of the presets.

[github-actions]

This issue has not had any activity in the past 60 days and will be closed in 365 days if not updated.

[Phemisters]

No planning any further changes for this.