chore: update instance list

[vlnst]

Add two new instances and remove ones that no longer respond.

• Add o.307200.xyz
• Add overflow.manerakai.com
• Remove the dead instances reported in [INSTANCES] Dead instances #167 (overflow.datura.network onion; the other domains in the report were not in the list)
• Remove ao.vern.cc, its onion, ao.pk47 onion and overflow.darknessrdor onion, all unreachable (tested 09.10.26)
• Fix the trailing comma that made instances.json invalid JSON

All remaining instances were checked and respond (tested 09.10.26), except the i2p one, which was not checked, and a.opnxng.com, which is kept: the operator announced on 09.10 (https://about.opnxng.com/blog/) that their servers are being migrated and services are coming back.

Closes #176
Closes #186
Closes #167