docs build remove mock after D45600232

Summary: We now use unittest.mock

Reviewed By: shapovalov

Differential Revision: D45868799

fbshipit-source-id: cd1042dc2c49c82c7b9e024f761c496049a31beb

docs/README.md

@@ -3,7 +3,7 @@
 ### Install dependencies
 
 ```
-pip install -U recommonmark mock sphinx sphinx_rtd_theme sphinx_markdown_tables
+pip install -U recommonmark sphinx sphinx_rtd_theme sphinx_markdown_tables
 ```
 
 ### Add symlink to the root README.md

docs/requirements.txt

@@ -3,7 +3,6 @@ Sphinx>=1.7
 recommonmark==0.4.0
 sphinx_rtd_theme
 sphinx_markdown_tables
-mock
 numpy
 iopath
 fvcore