Fix removeEventListener error (PixiJS 7)

[richardsolomou]

Fixes #438

This pull request adds an optional chaining operator to the events.domElement property when calling removeEventListener. This means that this will no longer error out when the Pixi prematurely destroys the domElement ahead of pixi-viewport.

Also removes the need to do this in userland for @pixi/react:

willUnmount: (viewport: PixiViewport) => {
    viewport.options.noTicker = true;
    viewport.destroy({ children: true });
}

I've tested this locally using pnpm patch on my application and it works wonders.

[davidfig]

Thanks!