Move report_assistant_event into language_model crate (#25508)

This PR moves the `report_assistant_event` function from the
`language_models` crate to the `language_model` crate.

This allows us to drop some dependencies on `language_models`.

Release Notes:

- N/A

crates/assistant/Cargo.toml

@@ -43,7 +43,6 @@ indoc.workspace = true
 language.workspace = true
 language_model.workspace = true
 language_model_selector.workspace = true
-language_models.workspace = true
 log.workspace = true
 lsp.workspace = true
 menu.workspace = true