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: Id417aaae518b18d220998ed6520fd729fec0a501

setup.cfg

@@ -6,6 +6,7 @@ description-file =
 author = OpenStack
 author-email = openstack-discuss@lists.openstack.org
 home-page = https://docs.openstack.org/python-searchlightclient/latest
+python-requires = >=3.6
 classifier =
     Environment :: OpenStack
     Intended Audience :: Information Technology
@@ -13,6 +14,8 @@ 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
@@ -30,13 +33,6 @@ openstack.search.v1 =
     search_facet_list = searchlightclient.osc.v1.facet:ListFacet
     search_query = searchlightclient.osc.v1.search:SearchResource
 
-[global]
-setup-hooks =
-    pbr.hooks.setup_hook
-
-[wheel]
-universal = 1
-
 [extract_messages]
 keywords = _ gettext ngettext l_ lazy_gettext
 mapping_file = babel.cfg

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)