[Kamilbenkirane]

OpenAIImagesEndpoint.CREATE_VARIATION (/v1/images/variations) is unused: no client, mapper or test references it. OpenAI's Create image variation reference says "This endpoint is retired and no longer available", and its model parameter reads "The legacy model used by the retired image variations endpoint. This endpoint no longer accepts requests." Two docstrings in the same wire client still name gpt-image-1, whose registration #553 removed.

Fix:

• src/celeste/providers/openai/images/config.py: drop OpenAIImagesEndpoint.CREATE_VARIATION.
• src/celeste/providers/openai/images/client.py (OpenAIImagesClient): drop "Streaming is only supported for gpt-image-1." from _make_stream_request and "gpt-image-1 returns usage, DALL-E models don't." from _parse_usage.
• No CHANGELOG line: dead code with no behavior change, same as fix(openai): remove the shut-down gpt-image-1 registration #553, fix(google): remove the shut-down veo-3.1-fast-generate-preview registration #552 and fix(google): remove the shut-down veo-3.1-lite-generate-preview registration #550.

Validation:

• Repo-wide grep: no other reference to CREATE_VARIATION, images/variations or gpt-image-1 outside the gpt-image-1-mini / gpt-image-1.5 ids.
• make ci passes (763 tests).
• No live call: the diff removes an unused enum member and two docstring lines.