passes on edge dialect will be done via tranform (#236)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/236

For graph transform in edge dialect, let's use `transform`. Also we don't expect any transform from aten to edge as discussed {F1081902441}

Reviewed By: angelayi

Differential Revision: D48911694

fbshipit-source-id: 3f895b6e8266511b38c0521066bea5c681080a30