Android LLM runner should avoid having deps on examples/models/{llama/llava} code

[kirklandsign]

🚀 The feature, motivation and pitch

When we build Android AAR and build the LLM part, right now it depends on examples/models/{llama/llava} code.

https://github.com/pytorch/executorch/blob/main/extension/android/CMakeLists.txt#L138-L150

Ideally, we should depend on production code under extension/llm, not examples/...

cc @cbilgin @larryliu0820

Alternatives

No response

Additional context

No response

RFC (Optional)

No response