public void removeListener( @Nonnull EntityCapabilitiesListener listener ) {
        allUserCapabilitiesListeners.remove( listener );
    }
Removes a previously registered event listener, if such a listener is currently registered.

@param listener The event listener to be removed.
xmppserver/src/main/java/org/jivesoftware/openfire/entitycaps/EntityCapabilitiesManager.java