Revert "Fix argparse issue for RHEL 6.5."

This reverts commit d088fde2ea59423d153f32d65be684be62727232.

Since the underlying problem with argparse has been resolved 
in python 2.7 and filtering out argparse for python 2.6 has been removed,
there is no longer a need to explicitly install argparse for python 2.6.

Closes-bug: #1346364
Change-Id: If9534bf5a4400f5f72475c67a8e6e14da08f9562
Merge "Revert "Fix argparse issue for RHEL 6.5.""