swarm: make sure appdata/contacts is synced with appdata/convInfo

On older versions, removeConversation didn't update appdata/contacts
causing some removed conversations to be announced in contacts details.
On Android, this hide the contact from the smartlist, as it's waiting
for a removed conversation.

Change-Id: I05be12ffcd2e5fe38d84c6f972b97e082c612ac7
GitLab: #714