fix: DeepSeek provider: mark retired aliases deepseek-v4-flash and deepseek-v4-flash-vision-exp as status = deprecated - #7727

Summary

Marks the first-party DeepSeek legacy aliases deepseek-v4-flash and deepseek-v4-flash-vision-exp as retired so they no longer surface as first-class models. DeepSeek serves only deepseek-flash and deepseek-v4-pro; the two old names are still callable but served by DeepSeek-V4.1-Flash at the Flash price.

Changes

• providers/deepseek/models/deepseek-v4-flash.toml: replaced placeholder ## mark as deprecated soon / # status = "deprecated" with status = "deprecated" (was absent/commented, now deprecated).
• providers/deepseek/models/deepseek-v4-flash-vision-exp.toml: replaced placeholder ## mark as deprecated soon / # status = "deprecated" with status = "deprecated" (was absent/commented, now deprecated).
• No cost, base_model, reasoning_options, or interleaved changes.

Evidence

• https://api-docs.deepseek.com/quick_start/pricing — Model Details table lists only deepseek-flash (version DeepSeek-V4.1-Flash) and deepseek-v4-pro (version DeepSeek-V4-Pro-0813).
• Same page, footnote (1): "The legacy names deepseek-v4-flash and deepseek-v4-flash-vision-exp are still accepted, but the corresponding models have been retired, their requests are served by the DeepSeek-V4.1-Flash model and billed at the Flash price." This directly supports status = "deprecated" on both alias files.
• Both files already carried a leading header comment citing the same pricing URL and describing the retired-alias behavior; that header was left intact.

Validation

• Read both edited provider TOMLs and confirmed status = "deprecated" is a top-level provider-only key alongside base_model/name, with placeholder comments removed.
• Fetched the DeepSeek pricing page live and verified the two-model table and retirement footnote quoted above.
• Did not run bun validate or any shell commands (not permitted in this environment).

Review notes

• None. Intentionally left deepseek-flash and deepseek-v4-pro untouched.

Closes #7726

Automated by the issue fixer: https://github.com/anomalyco/models.dev/actions/runs/35702376199