Remove dependents of language_models (#25511)

This PR removes the dependents of the `language_models` crate.

The following types have been moved from `language_models` to
`language_model` to facilitate this:

- `LlmApiToken`
- `RefreshLlmTokenListener`
- `MaxMonthlySpendReachedError`
- `PaymentRequiredError`

With this change only `zed` now depends on `language_models`.

Release Notes:

- N/A

crates/assistant_context_editor/Cargo.toml

@@ -30,7 +30,6 @@ indexed_docs.workspace = true
 language.workspace = true
 language_model.workspace = true
 language_model_selector.workspace = true
-language_models.workspace = true
 log.workspace = true
 multi_buffer.workspace = true
 open_ai.workspace = true