remove unused import in tutorial 4 addition to #18915 (closed)

First, open the ``polls/urls.py`` URLconf. It looks like this, according to the

tutorial so far::

    from django.conf.urls import patterns, include, url

    from django.conf.urls import patterns, url

    urlpatterns = patterns('polls.views',

        url(r'^$', 'index'),

Change it like so::

    from django.conf.urls import patterns, include, url

    from django.conf.urls import patterns, url

    from django.views.generic import DetailView, ListView

    from polls.models import Poll