docs: remove broken error-handling overlay screenshot (#93279)
The Cloudinary URL for the overlay screenshot
(`assets.vercel.com/image/upload/v1645118290/docs-assets/static/docs/error-handling/overlay.png`)
404s. The line above it had a `{/* TODO UPDATE SCREENSHOT */}` comment,
so this was already flagged as known-stale.
Removes the broken image and its `"Here is an example of an overlay:"`
intro line. The paragraph above still explains what the overlay is, so
the page reads cleanly without the screenshot. If someone produces a
fresh screenshot later, restoring the markdown with an updated URL is a
one-line change.
### Affects
-
`nextjs.org/docs/pages/building-your-application/configuring/error-handling`
(stable, on next stable cut)
-
`nextjs.org/docs/canary/pages/building-your-application/configuring/error-handling`
(canary)
### Older versions
The same broken URL is present in v13/v14/v15 of the docs (synced from
the corresponding release tags). Backport is a separate call for
maintainers.
