Revert D27833189: ns for fx: allow user functions in shadowing
Test Plan: revert-hammer
Differential Revision:
D27833189 (https://github.com/pytorch/pytorch/commit/19173509779cd5281d066463bc93b3bb4f620a1d)
Original commit changeset: dac418e294d1
fbshipit-source-id: c6f58dac1a35806ea7d1dfb993d67e698196dee1
