Governance related cleanup

[OriolAbril]

Description

I reviewed the governance doc while preparing https://discourse.pymc.io/t/steering-council-election-results/8391 so decided to remove some pieces that are outdated and not in use out and add a couple small clarifications.

Type of change

• [ ] New feature / enhancement
• [ ] Bug fix
• [ ] Documentation
• [ ] Maintenance
• [x] Other (please specify): governance

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📚 Documentation preview 📚: https://pymc--7541.org.readthedocs.build/en/7541/