- When cancelling group, do this:
1) remove self handle giving a reason
2) close channel
- Provided an enum of generic reasons for cancelling the group
- Removed not needed on_closed() callback in Chat object.
NOTE: This MRs should be landed along with https://code.launchpad.net/~ningbo-team/ningbo/set-reason-when-cancelling-group/+merge/302508.
Approved by Tiago Salem Herrmann, system-apps-ci-bot.