[api-ref] Remove temporary block

The os-api-ref 1.0.0 is out. We can remove the support to older
version now.
Reference: https://github.com/openstack/senlin/commit/
6d41feb58dd836d426c9b6f025846dbbf7295097
https://review.openstack.org/#/c/362170/

Change-Id: I6a900ecb38633ec118857fcd1c17c4d24495cab1

api-ref/source/conf.py

@@ -29,35 +29,17 @@ import subprocess
 import sys
 import warnings
 
-# TODO(Graham Hayes): Remove the following block of code when os-api-ref is
-# using openstackdocstheme
+import openstackdocstheme
 
-import os_api_ref
+extensions = [
+    'os_api_ref',
+]
 
-if getattr(os_api_ref, 'THEME', 'olsosphinx') == 'openstackdocstheme':
-    # We are on the new version with openstackdocstheme support
-
-    extensions = [
-        'os_api_ref',
-    ]
-
-    import openstackdocstheme  # noqa
-
-    html_theme = 'openstackdocs'
-    html_theme_path = [openstackdocstheme.get_html_theme_path()]
-    html_theme_options = {
-        "sidebar_mode": "toc",
-    }
-
-else:
-    # We are on the old version without openstackdocstheme support
-
-    extensions = [
-        'os_api_ref',
-        'oslosphinx',
-    ]
-
-# End temporary block
+html_theme = 'openstackdocs'
+html_theme_path = [openstackdocstheme.get_html_theme_path()]
+html_theme_options = {
+    "sidebar_mode": "toc",
+}
 
 # 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