message: Fix disconnecting (https://github.com/enso-org/ide/pull/854)
  Implement the "connection removed" event properly.
  Original commit:
diff: @@ -1314,6 +1314,7 @@ impl GraphEditorModel {
  self.refresh_edge_position(edge_id);
  self.refresh_edge_source_size(edge_id);
  }
  +
  }
  }
  @@ -1987,9 +1988,13 @@ fn new_graph_editor(app:&Application) -> GraphEditor {
  eval edge_source_click (((edge_id, _)) model.remove_edge_source(*edge_id));
  eval edge_target_click (((edge_id, _)) model.remove_edge_target(*edge_id));
  + outputs.edge_source_unset <+ edge_source_click.map(|(edge_id,_)| *edge_id);
  + outputs.edge_target_unset <+ edge_target_click.map(|(edge_id,_)| *edge_id);
  +
  }
  // === Edge creation ===
  +
  frp::extend! { network
  on_node_output_touch <- node_output_touch.down.constant(());
  @@ -2432,7 +2437,9 @@ fn new_graph_editor(app:&Application) -> GraphEditor {
  both_endpoints_set <- edge_endpoint_set.map(f!((id) model.is_connection(id)));
  new_connection <- edge_endpoint_set.gate(&both_endpoints_set);
  outputs.connection_added <+ new_connection;
  - outputs.connection_removed <+ outputs.edge_removed;
  + outputs.connection_removed <+ any
  + (outputs.edge_removed,outputs.edge_source_unset,outputs.edge_target_unset);
  + trace outputs.connection_removed;
  // === Status ===
  