Don't include python modules twice in package iteration.
Don't include python modules twice in package iteration.

This can be seen in the ports list, for example.

BUG=none
R=sbc@chromium.org

Review URL: https://codereview.chromium.org/565463002

Schibum/naclports,kuscsik/naclports,Schibum/naclports,Schibum/naclports,Schibum/naclports,kuscsik/naclports,yeyus/naclports,dtkav/naclports,Schibum/naclports,yeyus/naclports,yeyus/naclports,dtkav/naclports,dtkav/naclports,yeyus/naclports,kuscsik/naclports,kuscsik/naclports,yeyus/naclports,Schibum/naclports,dtkav/naclports,kuscsik/naclports,yeyus/naclports,dtkav/naclports