Deletes the benchmark's prompt embedding map.

Restricted to platform staff, matching the compute action it undoes. Removes the map and its points, so the anonymous read route goes back to answering 204 No Content and the public Prompts tab stops showing a figure. The cached prompt embedding vectors are a shared (model, text) cache and are left in place, so a later recomputation still reuses them.

Responds with 404 Not Found when the benchmark has no map. Safe to call while a computation is in flight: the running job writes back by id and simply finds nothing once the row is gone.