Remove unused CNCF mailing lists?

[trask]

These three CNCF mailing lists are very rarely used:

• https://lists.cncf.io/g/cncf-opentelemetry-community/topics
• https://lists.cncf.io/g/cncf-opentelemetry-contributors/topics
• https://lists.cncf.io/g/cncf-opentelemetry-comms/topics

and occasionally lead to confusion with users posting questions that go unmonitored/unanswered.

I'd suggest that we remove these three mailing lists from the community README and disable posting to them.

If we think the ability to send out an email blast is useful, we could introduce a new mailing list just for that, something like cncf-opentelemetry-announce.