Avoid repeat initialization

[andy-sweet]

As part of the React migration, one of the effects only occurs on mounting. In the production app, this will only ever be called once. But in development (and potentially in future versions of the app) it is called twice, which at best is wasteful and at worst may introduce in bugs.

The goal of this issue is to remove the second call to this.

See a recent PR comment for more context

[andy-sweet]

I made an attempt at initialize the PointCanvas once in app.tsx (instead of the mount effect in scene.tsx) and passing that through, but I could get the Scene component to re-render on width changes. And generally, this did not feel much better or a good use of time right now.