Simplify gen_oplist_copy_from_core file (#3549)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/3549

Looks like we just need the yaml file. That means, we can get rid off gen_supported_mobile_models and write_selected_mobile_ops and all its dependencies.

Reviewed By: lucylq

Differential Revision: D57122006

fbshipit-source-id: 07a0aafb686237cae29d774e552eddccce797136