contact_list: erase trust request via sync

If a contact is added, the first device will erase the trust request,
but the second device will update the contact but not the trust
request. Causing, the removeContact to generate a new request for
the previously created conversation.

Change-Id: I2f0a48b3c6b6b18ed6218e7a08c61de2beb08d3d
GitLab: #664