This PR removes the individual URL overrides for the LLM service.

We initially had `ZED_PREDICT_EDITS_URL` to allow for directing traffic
to the LLM Worker back when there was still the split of the
Collab-based LLM Service and the Cloudflare-based LLM Worker.

But now that all of the LLM functionality has been moved into the
Worker, we can just direct all traffic there.

Release Notes:

- N/A