fix: inference providers still using tools with tool_choice="none" (#2048)

# What does this PR do?

In our OpenAI API verification tests, some providers were still calling
tools even when `tool_choice="none"` was passed in the chat completion
requests. Because they aren't all respecting `tool_choice` properly,
this adjusts our routing implementation to remove the `tools` and
`tool_choice` from the request if `tool_choice="none"` is passed in so
that it does not attempt to call any of those tools. Adjusting this in
the router fixes this across all providers.

This also cleans up the non-streaming together.ai responses for tools,
ensuring it returns `None` instead of an empty list when there are no
tool calls, to exactly match the OpenAI API responses in that case.

## Test Plan

I observed existing failures in our OpenAI API verification suite - see

https://github.com/bbrowning/llama-stack-tests/blob/main/openai-api-verification/2025-04-27.md#together-llama-stack
for the failing `test_chat_*_tool_choice_none` tests. All streaming and
non-streaming variants were failing across all 3 tested models.

After this change, all of those 6 failing tests are now passing with no
regression in the other tests.

I verified this via:

```
llama stack run --image-type venv \
  tests/verifications/openai-api-verification-run.yaml
```

```
python -m pytest -s -v \
  'tests/verifications/openai_api/test_chat_completion.py' \
  --provider=together-llama-stack
```

The entire verification suite is not 100% on together.ai yet, but it's
getting closer.

This also increased the pass rate for fireworks.ai, and did not regress
the groq or openai tests at all.

Signed-off-by: Ben Browning <bbrownin@redhat.com>

llama_stack/providers/remote/inference/ollama/ollama.py

@@ -447,12 +447,6 @@ class OllamaInferenceAdapter(
         user: str | None = None,
     ) -> OpenAIChatCompletion | AsyncIterator[OpenAIChatCompletionChunk]:
         model_obj = await self._get_model(model)
-
-        # ollama still makes tool calls even when tool_choice is "none"
-        # so we need to remove the tools in that case
-        if tool_choice == "none" and tools is not None:
-            tools = None
-
         params = {
             k: v
             for k, v in {