[CMake] Duplicated sources in extension_llm_runner and llama_runner

[kirklandsign]

🐛 Describe the bug

These sources appeared twice:
extension/llm/runner/text_decoder_runner.cpp
extension/llm/runner/text_prefiller.cpp
extension/llm/sampler/sampler.cpp

Should llama_runner use llm/runner deps?

Versions

main 1984c5f

cc @larryliu0820 @jathu