team: don't try to connect to teamd in update_connection()
In constructed(), NMDevice starts watching the D-Bus name owner or
monitoring the unix socket, and so it is always aware if teamd is
running. When it is, NMDevice connects to it and initializes
priv->tdc.
It is not useful to try to connect to teamd in update_connection() because warnings will be generated by NM and by libteam if teamd is not running. As explained above the connection is always initialized when teamd is available, and so we can just check priv->tdc.