adb: remove adisconnect in aremotesocket.

The function of remote_socket_disconnect() is to make sure
the local_sockets and remote_sockets are closed when the binded
transport is disconnected. However, as we call close_all_sockets()
in handle_offline(), we don't need remote_socket_disconnect() any more.

Change-Id: I575f632d9f8703149f34e0210eb698a56e2516a9