Remove install unnecessary packages

The docs  requirements migrated to doc/requirements.txt
we need not install things from requirements.txt.

Change-Id: Ia0ae78adb7d96a3c38a26858b75c59bd419846a9

tox.ini

@@ -65,7 +65,6 @@ commands = python setup.py test --coverage --testr-args='{posargs}'
 
 [testenv:docs]
 deps =
-  -r {toxinidir}/requirements.txt
   -r {toxinidir}/test-requirements.txt
   -r {toxinidir}/doc/requirements.txt
 commands=