NodeRemovalDispatcher::dispatch should not use ownerDocument

ownerDocument is a silly DOM concept that's the document for all nodes
except the document itself where it's null. There's no reason to be
using that in the NodeRemovalDispatcher.

Review URL: https://codereview.chromium.org/299703010

git-svn-id: svn://svn.chromium.org/blink/trunk@174580 bbb929c8-8fbe-4397-9dbb-9b2b20218538