remove access to discontinued OpenAI models

[LucasLarson]

remove Zsh codex while there’s no obvious code-completion successor:

OpenAI has discontinued code-davinci models:

On March 23rd, we will discontinue support for the Codex API. All customers will have to transition to a different model. Codex was initially introduced as a free limited beta in 2021, and has maintained that status to date. Given the advancements of our newest GPT-3.5 models for coding tasks, we will no longer be supporting Codex and encourage all customers to transition to GPT-3.5-Turbo.

On March 23rd, we will discontinue support for the Codex API. All customers will have to transition to a different model. Codex was initially introduced as a free limited beta in 2021, and has maintained that status to date. Given the advancements of our newest GPT-3.5 models for coding tasks, we will no longer be supporting Codex and encourage all customers to transition to GPT-3.5-Turbo.

Models affected
The following models will be discontinued:

code-cushman:001
code-cushman:002
code-davinci:001
code-davinci:002

We understand this transition may be temporarily inconvenient, but we are confident it will allow us to increase our investment in our latest and most capable models.

Originally posted by @oyale in tom-doerr/zsh_codex#16 (comment)