sockets: remove obsolete code that updated listen address

When listening on unix/tcp sockets there was optional code that would update
the original SocketAddress struct with the info about the actual address that
was listened on. Since the conversion of everything to QIOChannelSocket, no
remaining caller made use of this feature. It has been replaced with the ability
to query the listen address after the fact using the function
qio_channel_socket_get_local_address. This is a better model when the input
address can result in listening on multiple distinct sockets.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Message-Id: <20171212111219.32601-1-berrange@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>