cfilters: kill connection filter events attach+detach

cfilters: kill connection filter events attach+detach

Make transfer attach/detach to/from connections chepaer.

- the "attach" event was no longer implemented by any filter
- the "detach" did the same as the "done" event for the filters
  who still implemented it. It should be superfluous as the "done"
  must always happen.

Closes #16067