docs: remove invalid og image cases (#66355)
### What
Removing the `/[...catchall]/<metadata image convention>.js` case from
docs
### Why
Since og image and icon routes are using catch-all routes to handle the
both single or multiple routes. For instance:
`app/opengraph-image.js` can possibly generate two cases:
- single route: `/opengraph-image`
- multi routes with `generateImageMetadata()`: `/opengraph-image/[id]`
We're not able to detect if there's `generateImageMetadata` defined in
the file before mapping the routes, and decided to create the different
routes to either `/opengraph-image` or `/opengraph-image/[id]`. That's
why we're using a catch-all routes to handle them rn.
Related #48106
Related #57349
