Switch to newer openstackdocstheme version

Switch to openstackdocstheme 2.2.1 version. Using
this version will allow especially:
* Linking from HTML to PDF document
* Allow parallel building of documents
* Fix some rendering problems

Update Sphinx version as well.

Change pygments_style to 'native' since old theme version always used
'native' and the theme now respects the setting and using 'sphinx' can
lead to some strange rendering.

Remove docs requirements from lower-constraints, they are not needed
during install or test but only for docs building.

openstackdocstheme renames some variables, so follow the renames
before the next release removes them. A couple of variables are also
not needed anymore, remove them.

See also
http://lists.openstack.org/pipermail/openstack-discuss/2020-May/014971.html

Change-Id: Ia9d81ddc1f3234af352787363e2963f808dbbad0

doc/requirements.txt

@@ -1,5 +1,5 @@
 # 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.
-openstackdocstheme>=1.20.0 # Apache-2.0
-sphinx!=1.6.6,!=1.6.7,!=2.1.0,>=1.6.2 # BSD
+openstackdocstheme>=2.2.1 # Apache-2.0
+sphinx>=2.0.0,!=2.1.0 # BSD

doc/source/conf.py

@@ -37,6 +37,10 @@ master_doc = 'index'
 # General information about the project.
 copyright = u'2013, OpenStack Foundation'
 
+# openstackdocstheme options
+openstackdocs_repo_name = 'openstack/heat-translator'
+openstackdocs_use_storyboard = True
+
 # If true, '()' will be appended to :func: etc. cross-reference text.
 add_function_parentheses = True
 
@@ -45,7 +49,7 @@ add_function_parentheses = True
 add_module_names = True
 
 # The name of the Pygments (syntax highlighting) style to use.
-pygments_style = 'sphinx'
+pygments_style = 'native'
 
 # -- Options for HTML output --------------------------------------------------
 html_theme = 'openstackdocs'

lower-constraints.txt

@@ -32,7 +32,6 @@ msgpack-python==0.4.0
 munch==2.1.0
 netaddr==0.7.18
 netifaces==0.10.4
-openstackdocstheme==1.20.0
 openstacksdk==0.11.2
 os-client-config==1.28.0
 os-service-types==1.2.0
@@ -41,7 +40,6 @@ oslo.i18n==3.15.3
 oslo.log==3.36.0
 oslo.serialization==2.18.0
 oslo.utils==3.33.0
-oslosphinx==4.7.0
 oslotest==3.2.0
 pbr==2.0.0
 prettytable==0.7.2
@@ -64,8 +62,6 @@ requestsexceptions==1.2.0
 simplejson==3.5.1
 six==1.10.0
 snowballstemmer==1.2.1
-Sphinx==1.6.2
-sphinxcontrib-websupport==1.0.1
 stevedore==1.20.0
 testrepository==0.0.18
 testscenarios==0.4