Sunsetting docs review task

- [x] make list of already-sunset plugins:
    - https://docs.google.com/spreadsheets/d/1FtT88n83EBihDYea2O_ZaJsd9ZSdG6ug-lhiCCDZj_0/edit#gid=0
    - https://docs.google.com/document/d/1n-XB-Ya2vrfPNoo1LyDgQd-_LKe7QE32KPQbo6UetG0/edit#
- [ ] For each plugin, check:
    - largo.readthedocs.io
    - INN/docs
    - support.inn.org
    - labs.inn.org
    - largo.inn.org