BUG: remove new action option --upgrade-epd.

Its function is the same as 'epkpg epd', but it does not support the full functions
of 'enpkg epd' when user is not logged in, which can lead to a confusing exception.
Merge pull request #86 from enthought/unimplement-upgrade-epd

BUG: remove new action option --upgrade-epd.