Bump the openstackdocstheme extension to 1.20

Some options are now automatically configured by the version 1.20[1]:
- project
- html_last_updated_fmt
- latex_engine
- latex_elements

[1]https://docs.openstack.org/openstackdocstheme/latest/#using-the-theme

Change-Id: I61a08d6a822ba984987e639d4ca7fea205f7c541

doc/requirements.txt

@@ -1,7 +1,7 @@
 # This is required for the docs build jobs
 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 # Apache-2.0
+openstackdocstheme>=1.20.0 # Apache-2.0
 
 # This is required for the releasenotes build jobs
 reno # Apache-2.0

releasenotes/source/conf.py

@@ -45,7 +45,6 @@ source_suffix = '.rst'
 master_doc = 'index'
 
 # General information about the project.
-project = u'puppet-horizon Release Notes'
 copyright = u'2017, Puppet OpenStack Developers'
 
 # The version info for the project you're documenting, acts as replacement for
@@ -138,7 +137,6 @@ html_static_path = ['_static']
 
 # If not '', a 'Last updated on:' timestamp is inserted at every page bottom,
 # using the given strftime format.
-html_last_updated_fmt = '%Y-%m-%d %H:%M'
 
 # If true, SmartyPants will be used to convert quotes and dashes to
 # typographically correct entities.
@@ -183,17 +181,6 @@ htmlhelp_basename = 'puppet-horizonReleaseNotesdoc'
 
 # -- Options for LaTeX output ---------------------------------------------
 
-latex_elements = {
-# The paper size ('letterpaper' or 'a4paper').
-#'papersize': 'letterpaper',
-
-# The font size ('10pt', '11pt' or '12pt').
-#'pointsize': '10pt',
-
-# Additional stuff for the LaTeX preamble.
-#'preamble': '',
-}
-
 # Grouping the document tree into LaTeX files. List of tuples
 # (source start file, target name, title,
 #  author, documentclass [howto, manual, or own class]).