Remove fbcode/caffe2/mode (#46454)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/46454
we stopped syncing this folder to fbcode, and it's not been used. AIbench will use the ones in xplat.
Test Plan: zbgs fbcode/caffe2/mode/ find nothing
Reviewed By: xta0
Differential Revision: D24356743
fbshipit-source-id: 7e70a2181a49b8ff3f87e5be3b8c808135f4c527
