Remove comment (#19148)
Summary:
Remove pointer to nonexistent Note.
It is already removed in "Remove support for CUDNN 6 (#15851)"
Pull Request resolved: https://github.com/pytorch/pytorch/pull/19148
Differential Revision: D14891514
Pulled By: soumith
fbshipit-source-id: dd33cfefa3a21e18afae5b3992dea085adaabda8
