Remove setting of version/release from releasenotes

Release notes are version independent, so remove version/release
values. We've found that projects now require the service package
to be installed in order to build release notes, and this is entirely
due to the current convention of pulling in the version information.

Release notes should not need installation in order to build, so this
unnecessary version setting needs to be removed.

This is needed for new release notes publishing, see
I56909152975f731a9d2c21b2825b972195e48ee8 and the discussion starting
at
http://lists.openstack.org/pipermail/openstack-dev/2017-November/124480.html
.

Change-Id: Ib71b1e4cee4bc05fe098266fd06ac6a51611b002

releasenotes/source/conf.py

@@ -22,8 +22,6 @@
 # All configuration values have a default; values that are commented out
 # serve to show the default.
 
-import pbr.version
-
 # If extensions (or modules to document with autodoc) are in another directory,
 # add these directories to sys.path here. If the directory is relative to the
 # documentation root, use os.path.abspath to make it absolute, like shown here.
@@ -68,17 +66,13 @@ oslosphinx_cgit_link = (
     "https://git.openstack.org/cgit/openstack/{}".format(target_name)
 )
 
-# The version info for the project you're documenting, acts as replacement for
-# |version| and |release|, also used in various other places throughout the
-# built documents.
-#
+# Release notes are version independent
 # The short X.Y version.
-version_info = pbr.version.VersionInfo(target_name)
-# The full version, including alpha/beta/rc tags.
-release = version_info.version_string_with_vcs()
-# The short X.Y version.
-version = version_info.canonical_version_string()
 
+# The full version, including alpha/beta/rc tags.
+release = ''
+# The short X.Y version.
+version = ''
 # openstackdocstheme options
 repository_name = 'openstack/' + target_name
 bug_project = project.lower()