Swarm: remove a user from the conversation

• Implement https://git.jami.net/savoirfairelinux/ring-project/wikis/Group-chat-feature-(design-draft)#remove-a-device-from-a-conversation
• Add tests

added 1 deleted label

changed title from Swarm: remove a user from the conversation to Swarm: remove a user from the conversation (NEEDS DESIGN)

added SprintIn progress label

changed title from Swarm: remove a user from the conversation (NEEDS DESIGN) to Swarm: remove a user from the conversation

changed the description

added SprintTo review label and removed SprintIn progress label

added SprintIn progress label and removed SprintTo review label

added SprintTo review label and removed SprintIn progress label

mentioned in commit ce617494

closed

added swarm label