DOC: remove java documentation (#38920)
Summary:
Continuation of issue gh-36064 and PR gh-38042 which removed the unmaintained javaspinx extension. The unknown sphinx directives cause warnings when building documentation.
Edit: link to PR as well as issue
Pull Request resolved: https://github.com/pytorch/pytorch/pull/38920
Differential Revision: D21818297
Pulled By: ezyang
fbshipit-source-id: 2c1d007a7689b26653d7dee081b0b969b8a731a2
