use 3.19 version of cmake_dependent_option (#721)

Summary:
Remove `cmake-policy` because it's not compatible to cmake 3.19 and is breaking ARM demo.

Pull Request resolved: https://github.com/pytorch/executorch/pull/721

Reviewed By: digantdesai

Differential Revision: D50088065

Pulled By: larryliu0820

fbshipit-source-id: f7a8fca92b86e7b1d783ee86ba034e24d82f4d5b