Remove redundant generate_*_compile_spec funcs (#3869)

Summary:
tidying up a redundant wrapper function.

Pull Request resolved: https://github.com/pytorch/executorch/pull/3869

Reviewed By: mergennachin

Differential Revision: D58301772

Pulled By: digantdesai

fbshipit-source-id: cd906e2aa307408e7e2f877ace6544e91cd972fc