remove ez_setup import from setup.py

During the review for commit r1713 it was determined that ez_setup.py
was not going to be part of the commit.  While ez_setup.py was removed
as requested, the import and usage of ez_setup in setup.py was not
removed appropriately.  This change removes the import and usage so that
installing gyp via setuptools works as expected.

R=mark@chromium.org, scottmg@chromium.org

Review URL: https://codereview.chromium.org/24282003

Patch from Eric N. Vander Weele <ericvw@gmail.com>.

git-svn-id: http://gyp.googlecode.com/svn/trunk@1736 78cadc50-ecff-11dd-a971-7dbc132099af