Cleanup py27 support

This repo is now testing only with Python 3, so let's make
a few cleanups:
- Remove obsolete sections from setup.cfg
- Update requirements, no need for python_version anymore
- Use newer openstackdocstheme version, update other requirements

Change-Id: I2aec09250c96bc411d19cb6c1a1ee852394d39e5

requirements.txt

@@ -1,11 +1,10 @@
 # The order of packages is significant, because pip processes them in the order
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
-pbr>=1.0
+pbr>=2.0
 doc8>=0.6.0 # Apache-2.0
-openstackdocstheme>=1.18.1 # Apache-2.0
-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,>=1.6.2;python_version>='3.4'  # BSD
+openstackdocstheme>=1.31.2 # Apache-2.0
+sphinx!=1.6.6,!=1.6.7,>=1.6.2 # BSD
 stestr>=2.0.0 # Apache-2.0
 testtools>=0.9.36,!=1.2.0
 yasfb>=0.8.0

setup.cfg

@@ -10,14 +10,3 @@ classifier =
     Intended Audience :: Developers
     License :: OSI Approved :: Apache Software License
     Operating System :: POSIX :: Linux
-
-[build_sphinx]
-all_files = 1
-build-dir = doc/build
-source-dir = doc/source
-
-[pbr]
-warnerrors = True
-
-[wheel]
-universal = 1