chore!: deprecate eval/tasks (#1186)

# What does this PR do?
- Fully deprecate eval/tasks

[//]: # (If resolving an issue, uncomment and update the line below)
Closes #1088 

NOTE: this will be a breaking change. We have introduced the new API in
0.1.3 .

Notebook has been updated to use the new endpoints.

## Test Plan
```
pytest -v -s --nbval-lax ./docs/notebooks/Llama_Stack_Benchmark_Evals.ipynb 
```
<img width="611" alt="image"
src="https://github.com/user-attachments/assets/79f6efe1-81ba-494e-bf36-1fc0c2b9bc6f"
/>



cc @SLR722  for awareness

[//]: # (## Documentation)

llama_stack/apis/benchmarks/benchmarks.py

@@ -64,23 +64,3 @@ class Benchmarks(Protocol):
         provider_id: Optional[str] = None,
         metadata: Optional[Dict[str, Any]] = None,
     ) -> None: ...
-
-    @webmethod(route="/eval-tasks", method="GET")
-    async def DEPRECATED_list_eval_tasks(self) -> ListBenchmarksResponse: ...
-
-    @webmethod(route="/eval-tasks/{eval_task_id}", method="GET")
-    async def DEPRECATED_get_eval_task(
-        self,
-        eval_task_id: str,
-    ) -> Optional[Benchmark]: ...
-
-    @webmethod(route="/eval-tasks", method="POST")
-    async def DEPRECATED_register_eval_task(
-        self,
-        eval_task_id: str,
-        dataset_id: str,
-        scoring_functions: List[str],
-        provider_benchmark_id: Optional[str] = None,
-        provider_id: Optional[str] = None,
-        metadata: Optional[Dict[str, Any]] = None,
-    ) -> None: ...