Update plugins after core event changes.

dcc/src/com/dmdirc/addons/dcc/events/DccDisplayableEvent.java

 import com.dmdirc.events.DisplayableEvent;
 
 import java.util.Optional;
-import java.util.concurrent.atomic.AtomicReference;
 
 /**
  * Base class for displayable DCC events.
  */
 public abstract class DccDisplayableEvent extends DccEvent implements DisplayableEvent {
 
-    /** The display format to use for this event. */
-    private final AtomicReference<String> displayFormatRef = new AtomicReference<>("");
     /** The properties associated with this event. */
     private final DisplayPropertyMap properties = new DisplayPropertyMap();
 
-    @Override
-    public String getDisplayFormat() {
-        return displayFormatRef.get();
-    }
-
-    @Override
-    public void setDisplayFormat(final String format) {
-        displayFormatRef.set(format);
-    }
-
     @Override
     public <T> void setDisplayProperty(final DisplayProperty<T> property, final T value) {
         properties.put(property, value);

lagdisplay/src/com/dmdirc/addons/lagdisplay/LagDisplayManager.java

 import com.dmdirc.config.prefs.PreferencesSetting;
 import com.dmdirc.config.prefs.PreferencesType;
 import com.dmdirc.events.ClientPrefsOpenedEvent;
+import com.dmdirc.events.DisplayProperty;
 import com.dmdirc.events.ServerDisconnectedEvent;
 import com.dmdirc.events.ServerGotPingEvent;
 import com.dmdirc.events.ServerNoPingEvent;
             } catch (NumberFormatException ex) {
                 pings.remove(event.getConnection());
             }
-            event.setDisplayFormat("");
+            event.setDisplayProperty(DisplayProperty.DO_NOT_DISPLAY, true);
 
             panel.refreshDialog();
         }