Do not start netconf-impl for css netconf endpoint

netconf-impl project contains both implementation of APIs defined in
netconf-api and netconf-mapping-api projects and also instantiation
logic of some base netconf server components for netconf css northbound
endpoint. Remove this logic, css is not used anymore, so it is its
netconf endpoint.

Change-Id: Iad381885d229e374957d87087a4a96ba46f75551
Signed-off-by: Jakub Morvay <jmorvay@frinx.io>