Revert D27836064: ns for fx: add fp16 function shadowing
Test Plan: revert-hammer
Differential Revision:
D27836064 (https://github.com/pytorch/pytorch/commit/96a9eafcfb0e3ddc5458f37cebc72c6845489e00)
Original commit changeset: 37a434a04e2b
fbshipit-source-id: e85088f5e301e14a0fc9ac1f7241c2baaf0a957e
