Revert D25569586: stft: Change require_complex warning to an error
Test Plan: revert-hammer
Differential Revision:
D25569586 (https://github.com/pytorch/pytorch/commit/5874925b461b67094ecf60ab1ae4339ae3d48cfe)
Original commit changeset: 09608088f540
fbshipit-source-id: 6a5953b327a4a2465b046e29bb007a0c5f4cf14a
