Before we go ahead and remove the endpoints, we should check diagnostics to see what % of servers are still using the APIv3 endpoints (as of Nov 21st, it's about 20% but only a few servers have upgraded to v4.4).
If it's a large % we might want to consider taking a different strategy, e.g. disabling the APIv3 config setting for everyone in v4.6, but not removing the endpoints until a couple of months later to give them a bit more time for migration.
In addition to removing the endpoints, we should also make APIv3 docs less prominent, with a clear note that it's no longer supported.
No testing required