public MyGui() {
    ...
    MinecraftForge.EVENT_BUS.register(this);
    ...
}

@ForgeSubscribe
public void onPreRenderGameOverlay(RenderGameOverlayEvent.Pre event) {
    if (event.type == ElementType.HOTBAR) {
        event.setCanceled(true);
    }
}

@Override
public void onClosed() {
    ...
    MinecraftForge.EVENT_BUS.unregister(this);
    ...
}