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: Ibfae0a0e639ad13c7e547a815c2bf2c43a5b1673

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}