libnetwork: drop vestigial endpoint-rename logic

The logic to rename an endpoint includes code which would synchronize
the renamed service records to peers through the distributed datastore.
It would trigger the remote peers to pick up the rename by touching a
datastore object which remote peers would have subscribed to events on.
The code also asserts that the local peer is subscribed to updates on
the network associated with the endpoint, presumably as a proxy for
asserting that the remote peers would also be subscribed.
https://github.com/moby/libnetwork/pull/712

Libnetwork no longer has support for distributed datastores or
subscribing to datastore object updates, so this logic can be deleted.

Signed-off-by: Cory Snider <csnider@mirantis.com>

libnetwork/endpoint.go

@@ -589,13 +589,6 @@ func (ep *Endpoint) rename(name string) error {
 			return types.InternalErrorf("Could not delete service state for endpoint %s from cluster on rename: %v", ep.Name(), err)
 		}
 	} else {
-		c.mu.Lock()
-		_, ok = c.nmap[n.ID()]
-		c.mu.Unlock()
-		if !ok {
-			// FIXME(thaJeztah): what is this check for, or is this to prevent a race condition (network removed)?
-			return fmt.Errorf("watch null for network %q", n.Name())
-		}
 		n.updateSvcRecord(ep, false)
 	}
 
@@ -636,14 +629,6 @@ func (ep *Endpoint) rename(name string) error {
 	if err = c.updateToStore(ep); err != nil {
 		return err
 	}
-	// After the name change do a dummy endpoint count update to
-	// trigger the service record update in the peer nodes
-
-	// Ignore the error because updateStore fail for EpCnt is a
-	// benign error. Besides there is no meaningful recovery that
-	// we can do. When the cluster recovers subsequent EpCnt update
-	// will force the peers to get the correct EP name.
-	_ = n.getEpCnt().updateStore()
 
 	return err
 }