Use prerendered KaTeX in docs. (#23376)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/23376
This uses master version of sphinxcontrib-katex as it only
recently got prerender support.
Fixes #20984
Signed-off-by: Edward Z. Yang <ezyang@fb.com>
Test Plan: Imported from OSS
Differential Revision: D16582064
Pulled By: ezyang
fbshipit-source-id: 9ef24c5788c19572515ded2db2e8ebfb7a5ed44d
