Remove Python 2.6 classifier
Remove Python 2.6 classifier

We have decided to remove Python 2.6 support, this commit
removes Python 2.6 classifier before dropping any Python
2.6 support in code.

Change-Id: I5fc83f5b61c13cfedaf75f95037c7ff78005c6a6

openstack/oslotest,openstack/oslotest