Service health check and route table schema refs

Change the refs for service health check and route table from
service instance and vmi to derived. This removes the loop for
deletion from heat.

Change-Id: If10e7f11c4fcf14a390bac79b82c76a981dea128
Closes-Bug: #1565980

src/schema/vnc_cfg.xsd

@@ -1621,12 +1621,12 @@ targetNamespace="http://www.contrailsystems.com/2012/VNC-CONFIG/0">
 <xsd:element name="service-health-check-service-instance" type="ServiceInterfaceTag"/>
 <!--#IFMAP-SEMANTICS-IDL
      Link('service-health-check-service-instance',
-          'service-health-check', 'service-instance', ['ref']) -->
+          'service-health-check', 'service-instance', ['ref', 'derived']) -->
 
 <xsd:element name="interface-route-table-service-instance" type="ServiceInterfaceTag"/>
 <!--#IFMAP-SEMANTICS-IDL
      Link('interface-route-table-service-instance',
-          'interface-route-table', 'service-instance', ['ref']) -->
+          'interface-route-table', 'service-instance', ['ref', 'derived']) -->
 
 <xsd:element name="routing-policy-service-instance" type="RoutingPolicyServiceInstanceType"/>
 <!--#IFMAP-SEMANTICS-IDL