Remove install unnecessary packages

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

Change-Id: I7990b24861546bcc54f3286e57e22b8acd270382

tox.ini

@@ -25,7 +25,6 @@ commands = {posargs}
 [testenv:docs]
 deps =
   -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
-  -r{toxinidir}/requirements.txt
   -r{toxinidir}/doc/requirements.txt
 commands = sphinx-build -v -W -b html -d doc/build/doctrees doc/source doc/build/html