Fix Sphinx warning about '_images' not existing (#27927)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/27927
This fixes
`WARNING: html_static_path entry '_images' does not exist`
by removing '_images' from conf.py. As far as I can tell, '_images' in
`html_static_path` is only necessary if images already exist in the
`_images` folder; otherwise, sphinx is able to auto-generate _images
into the build directory and populate it correctly.
Test Plan: - build and view the docs locally.
Differential Revision: D17915109
Pulled By: zou3519
fbshipit-source-id: ebcc1f331475f52c0ceadd3e97c3a4a0d606e14b
