switch documentation job to new PTI

This is a mechanically generated patch to switch the documentation
jobs to use the new PTI versions of the jobs as part of the
python3-first goal.

See the python3-first goal document for details:
https://governance.openstack.org/tc/goals/stein/python3-first.html

Change-Id: I766b9d504ea24e1fadaad0d158da43012a07290a
Story: #2002586
Task: #24328

.zuul.yaml

@@ -1,4 +1,4 @@
 - project:
     templates:
       - openstack-python-jobs
-      - publish-openstack-sphinx-docs
+      - publish-openstack-docs-pti

doc/source/conf.py

@@ -29,7 +29,6 @@ sys.path.insert(0, os.path.abspath('../..'))
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
 # ones.
 extensions = [
-    'rst2pdf.pdfbuilder',
     'sphinx.ext.autodoc',
     'sphinxcontrib.httpdomain',
     'openstackdocstheme',

requirements.txt

@@ -1,7 +1,6 @@
 openstackdocstheme>=1.11.0  # Apache-2.0
 sphinx>=1.6.2 # BSD
 
-rst2pdf
 six>=1.9.0
 sphinxcontrib-httpdomain
 sphinx_rtd_theme

tox.ini

@@ -29,8 +29,7 @@ commands = flake8
 
 [testenv:docs]
 basepython = python3
-commands =
-    python setup.py build_sphinx
+commands = sphinx-build -b html doc/source doc/build/html
 
 [testenv:pdf]
 deps =