Remove unnecessary and dangerous sync_stream
Remove unnecessary and dangerous sync_stream

This sometimes meant the event caused by sending the data was swallowed,
breaking tests that expected something to happen after calling send_data

Reviewed-by: Guillaume Desmottes <f16649c7afcd84e3350287183c4ed23cb1aea57c@collabora.co.uk>

Ziemin/telepathy-gabble,community-ssu/telepathy-gabble,community-ssu/telepathy-gabble,Ziemin/telepathy-gabble,jku/telepathy-gabble,jku/telepathy-gabble,Ziemin/telepathy-gabble,mlundblad/telepathy-gabble,jku/telepathy-gabble,mlundblad/telepathy-gabble,community-ssu/telepathy-gabble,community-ssu/telepathy-gabble,Ziemin/telepathy-gabble,mlundblad/telepathy-gabble