Remove PopupContainerSettings now that there is only one type of popup that Chrome renders.

BUG=330077
TEST=<select> menus continue to work correctly
R=tkent@chromium.org

Review URL: https://codereview.chromium.org/112233003

git-svn-id: svn://svn.chromium.org/blink/trunk@164348 bbb929c8-8fbe-4397-9dbb-9b2b20218538