Deprecate `/v1/inspect/providers`

[cdoern]

🚀 Describe the new functionality needed

now that /v1/providers is a top level API offering inspection and listing: #1429

we should deprecate /v1/inspect/providers which is the same as v1/providers/.

This should entail:

1. removing the webmethod in api/inspect.py
2. removing documentation in llama-stack-spec.yaml and llama-stack-spec.html
3. removing associated methods in distribution/inspect.py
4. amending unit tests.

💡 Why is this needed? What if we don't build it?

Leaving both methods is duplicative and /v1/providers is more RESTful

Other thoughts

This should be done in roughly 2 weeks such that this change is not lost over time