test: 移除已弃用的 Qwen 模型错误提示测试

清理测试代码中针对已弃用 `qwen-plus` 模型的错误提示断言，
该模型现已使用 `qwen/qwen-plus` 格式，相关提示逻辑已移除。

rust/crates/rusty-claude-cli/src/main.rs

@@ -10440,21 +10440,6 @@ mod tests {
             err_gpt.contains("OPENAI_API_KEY"),
             "GPT model error should mention env var: {err_gpt}"
         );
-        let err_qwen = parse_args(&[
-            "prompt".to_string(),
-            "test".to_string(),
-            "--model".to_string(),
-            "qwen-plus".to_string(),
-        ])
-        .expect_err("`--model qwen-plus` should fail with DashScope hint");
-        assert!(
-            err_qwen.contains("Did you mean `qwen/qwen-plus`?"),
-            "Qwen model error should hint qwen/ prefix: {err_qwen}"
-        );
-        assert!(
-            err_qwen.contains("DASHSCOPE_API_KEY"),
-            "Qwen model error should mention env var: {err_qwen}"
-        );
         // Unrelated invalid model should NOT get a hint
         let err_garbage = parse_args(&[
             "prompt".to_string(),