Remove unnecessary includes from collection / nodelist classes

Remove unnecessary includes from collection / nodelist classes to reduce
interdependency and make build time shorter in case of change.

R=adamk@chromium.org

Review URL: https://codereview.chromium.org/412533002

git-svn-id: svn://svn.chromium.org/blink/trunk@178690 bbb929c8-8fbe-4397-9dbb-9b2b20218538