Remove docs from linters

The openstack-ansible-linters job runs the linters tox environment - and
the docs jobs runs the docs environment.

Remove the docs jobs from the linters environment, there's no need to
run the docs jobs in both linters and docs environment, it just wastes
testing resources.

Change-Id: I6a07fa325dba33e5cb67da7e7bebf4ff75cab373

tox.ini

@@ -98,12 +98,9 @@ commands =
 
 [testenv:linters]
 basepython = python3
-deps =
-    -r{toxinidir}/doc/requirements.txt
 commands =
     bash -c "{toxinidir}/tests/common/test-ansible-env-prep.sh"
     {[testenv:pep8]commands}
     {[testenv:bashate]commands}
     {[testenv:ansible-lint]commands}
     {[testenv:ansible-syntax]commands}
-    {[testenv:docs]commands}