Switch to newer openstackdocstheme and reno versions

Switch to openstackdocstheme 2.1.2 and reno 3.1.0 versions. Using
these versions will allow parallelizing building of documents.

Update Sphinx version as well.

openstackdocstheme renames some variables, so follow the renames. A
couple of variables are also not needed anymore, remove them.
Remove duplicated variables.

Depends-On: https://review.opendev.org/728432
Change-Id: Icb604b31150a1ad6c29a9a4a934ed13f8a0b4976

doc/requirements.txt

@@ -1,10 +1,9 @@
 # The order of packages is significant, because pip processes them in the order
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
-sphinx!=1.6.6,!=1.6.7,>=1.6.2,<2.0.0;python_version=='2.7' # BSD
-sphinx!=1.6.6,!=1.6.7,!=2.1.0,>=1.6.2;python_version>='3.4' # BSD
-openstackdocstheme>=1.30.0 # Apache-2.0
-reno>=2.5.0 # Apache-2.0
+sphinx>=2.0.0,!=2.1.0 # BSD
+openstackdocstheme>=2.1.2 # Apache-2.0
+reno>=3.1.0 # Apache-2.0
 sphinxcontrib-apidoc>=0.2.0 # BSD
 
 # redirect tests in docs

doc/source/conf.py

@@ -36,10 +36,6 @@ autoclass_content = 'both'
 # The master toctree document.
 master_doc = 'index'
 
-# openstackdocstheme options
-repository_name = 'openstack/python-novaclient'
-bug_project = 'python-novaclient'
-bug_tag = 'doc'
 copyright = 'OpenStack Contributors'
 
 
@@ -70,10 +66,10 @@ latex_elements = {
 
 # -- Options for openstackdocstheme -------------------------------------------
 
-repository_name = 'openstack/python-novaclient'
-bug_project = 'python-novaclient'
-bug_tag = ''
-openstack_projects = [
+openstackdocs_repo_name = 'openstack/python-novaclient'
+openstackdocs_bug_project = 'python-novaclient'
+openstackdocs_bug_tag = ''
+openstackdocs_projects = [
     'keystoneauth',
     'nova',
     'os-client-config',