Remove the 2.6 classifier

Octavia is only targeting 2.7 and newer so it shouldn't
have the 2.6 classifier listed in its setup.cfg file.

Change-Id: I68fce657362a54b1953183cd6191d90ffa4815ce

setup.cfg

@@ -16,7 +16,6 @@ classifier =
     License :: OSI Approved :: Apache Software License
     Operating System :: POSIX :: Linux
     Programming Language :: Python
-    Programming Language :: Python :: 2.6
     Programming Language :: Python :: 2.7
 
 [build_sphinx]