Fix 'tox -ereleasenotes' Error

1. replace reno.sphinxtest with reno.sphinxext for Sphinx extensions as
sphinxtest is not supported
2. remove 'Indices and tables' from index.rst as it's not found.

Change-Id: Idb9e75a326e5b1fc39a28aebb6eb58182e4a27c5

releasenotes/source/conf.py

@@ -21,7 +21,7 @@ sys.path.insert(0, os.path.abspath('../..'))
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom ones.
 extensions = [
     'oslosphinx',
-    'reno.sphinxtest',
+    'reno.sphinxext',
 ]
 
 # autodoc generation is a bit aggressive and a nuisance when doing heavy

releasenotes/source/index.rst

@@ -12,10 +12,3 @@ Contents
    newton
    mitaka
    liberty
-
-
-   Indices and tables
-   ==================
-
-   * :ref:`genindex`
-     * :ref:`search`