Add buck file to selective build (#3812)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/3812

So we can build in xplat.

Also remove unused dependencies to scalar_utils.

Reviewed By: larryliu0820

Differential Revision: D57950299

fbshipit-source-id: f47a69a2edd2c8f66de9d9b42565d1f65d2b98c0