types/change: drop unused VisibilityChange

It fills PeersRemoved without deleting anything. The batcher now tears down
the session behind every removed id, so a caller would kill a live poll.

Updates #3410

hscontrol/types/change/change.go

@@ -340,15 +340,6 @@ func PolicyAndPeers(changedPeers ...types.NodeID) Change {
 	}
 }
 
-func VisibilityChange(reason string, added, removed []types.NodeID) Change {
-	return Change{
-		Reason:        reason,
-		IncludePolicy: true,
-		PeersChanged:  added,
-		PeersRemoved:  removed,
-	}
-}
-
 func PeersChanged(reason string, peerIDs ...types.NodeID) Change {
 	return Change{
 		Reason:       reason,

hscontrol/types/change/change_test.go

@@ -458,14 +458,6 @@ func TestPolicyAndPeers(t *testing.T) {
 	assert.Equal(t, []types.NodeID{1, 2, 3}, r.PeersChanged)
 }
 
-func TestVisibilityChange(t *testing.T) {
-	r := VisibilityChange("tag change", []types.NodeID{1}, []types.NodeID{2, 3})
-	assert.Equal(t, "tag change", r.Reason)
-	assert.True(t, r.IncludePolicy)
-	assert.Equal(t, []types.NodeID{1}, r.PeersChanged)
-	assert.Equal(t, []types.NodeID{2, 3}, r.PeersRemoved)
-}
-
 func TestPeersChanged(t *testing.T) {
 	r := PeersChanged("routes approved", 1, 2)
 	assert.Equal(t, "routes approved", r.Reason)