Remove obsolete environment.yml from pytorch_CycleGAN_and_pix2pix (#2664)

Summary:
This file is not used (requirements.txt is used instead), and it contains very old dependencies, tripping security checks at meta (e.g. see T248633570).

Pull Request resolved: #2664

Reviewed By: huydhn

Differential Revision: D91633984

Pulled By: izaitsevfb

fbshipit-source-id: 0cb0a88c1ed7e42285e485b1c02c87e30f3f9b5a

Author: izaitsevfb