[VNFD] Remove the virtual_link_reference from connection_points

[mbredel]

The connection-point parameter contains a reference to the virtual-link that is connected to it (and vice versa). This, however, creates a cyclic reference which is error prone.

Since it is the virtual links that create the VNFC, the reference in the connection points could be removed without any loss of information. However, this would contradict the ETSI NFV specification.

Should we remove the virtual link references form the connection points?