Remove Qwen2 model (#18444)

Removed deprecated Qwen2 7B Instruct model from zed.dev provider (staff
only).

Release Notes:

- N/A

crates/collab/src/llm/db/tests/provider_tests.rs

@@ -26,7 +26,6 @@ async fn test_initialize_providers(db: &mut LlmDatabase) {
             LanguageModelProvider::Anthropic,
             LanguageModelProvider::Google,
             LanguageModelProvider::OpenAi,
-            LanguageModelProvider::Zed
         ]
     )
 }