Move openstackdocstheme to extensions in api-ref

Move openstackdocstheme to extensions. According to the guide below: 
https://docs.openstack.org/openstackdocstheme/latest/

Change-Id: I09acab1026c621d29ba5076345f8facdf7cfd91f

api-ref/source/conf.py

@@ -30,16 +30,14 @@ import subprocess
 import sys
 import warnings
 
-import openstackdocstheme
-
 html_theme = 'openstackdocs'
-html_theme_path = [openstackdocstheme.get_html_theme_path()]
 html_theme_options = {
     "sidebar_mode": "toc",
 }
 
 extensions = [
     'os_api_ref',
+    'openstackdocstheme',
 ]
 
 # If extensions (or modules to document with autodoc) are in another directory,
@@ -78,13 +76,10 @@ release = version_info.release_string()
 # The short X.Y version.
 version = version_info.version_string()
 
-# Config logABug feature
-giturl = u'http://git.openstack.org/cgit/openstack/heat/tree/api-ref/source'
-# source tree
-# html_context allows us to pass arbitrary values into the html template
-html_context = {'bug_tag': 'api-ref',
-                'giturl': giturl,
-                'bug_project': 'heat'}
+# openstackdocstheme options
+repository_name = 'openstack/heat'
+bug_project = 'heat'
+bug_tag = 'api-ref'
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.