delete get_param and is_param from executorch codebase (#108)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/108

moved to export proper in D48361384

Reviewed By: tugsbayasgalan

Differential Revision: D48608700

fbshipit-source-id: e95ae1d5897534f00365e2cf5f0c4741455cc8d2