Remove unintentional raw_input() from policy_prefs_ui.py

Got unintentionally introduced in r144734

R=craigdh@chromium.org
BUG= 134560
TEST=

Review URL: https://chromiumcodereview.appspot.com/10701059

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@145163 0039d316-1c4b-4281-b951-d872f2087c98