This reverts commit d088fde2ea.
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