Cleanup py27 support

Make a few cleanups:
- Remove python 2.7 stanza from setup.py
- Add requires on python >= 3.6 to setup.cfg so that pypi and pip
  know about the requirement
- Remove obsolete sections from setup.cfg:
  * Wheel is not needed for python 3 only repo
  * Some other sections are obsolete
- Update classifiers

Change-Id: I6f458fb60b5a33b5aa2ce3ab292862ab98eb4670

setup.cfg

@@ -12,6 +12,7 @@ project_urls =
     API Reference = https://docs.openstack.org/api-ref/placement/
     Source Code = https://opendev.org/openstack/placement
     Release Notes = https://docs.openstack.org/releasenotes/placement/
+python-requires = >=3.6
 classifier =
     Environment :: OpenStack
     Intended Audience :: Information Technology
@@ -19,14 +20,12 @@ classifier =
     License :: OSI Approved :: Apache Software License
     Operating System :: POSIX :: Linux
     Programming Language :: Python
+    Programming Language :: Python :: Implementation :: CPython
+    Programming Language :: Python :: 3 :: Only
     Programming Language :: Python :: 3
     Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7
 
-[global]
-setup-hooks =
-    pbr.hooks.setup_hook
-
 [files]
 packages =
     placement
@@ -51,11 +50,3 @@ console_scripts =
     placement-status = placement.cmd.status:main
 wsgi_scripts =
     placement-api = placement.wsgi:init_application
-
-[egg_info]
-tag_build =
-tag_date = 0
-tag_svn_revision = 0
-
-[wheel]
-universal = 1

setup.py

@@ -13,17 +13,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-# THIS FILE IS MANAGED BY THE GLOBAL REQUIREMENTS REPO - DO NOT EDIT
 import setuptools
 
-# In python < 2.7.4, a lazy loading of package `pbr` will break
-# setuptools if some other modules registered functions in `atexit`.
-# solution from: http://bugs.python.org/issue15881#msg170215
-try:
-    import multiprocessing  # noqa
-except ImportError:
-    pass
-
 setuptools.setup(
     setup_requires=['pbr>=2.0.0'],
     pbr=True)