Remove needsNotifyRemoveAllPendingStylesheet

After r174347 we don't execute script blocked on stylesheets synchronously
inside ::removedFrom so we can remove this special case inside the
ChildNodeRemovalNotifier.

This code was originally added in
http://trac.webkit.org/changeset/125988

Review URL: https://codereview.chromium.org/295993005

git-svn-id: svn://svn.chromium.org/blink/trunk@174421 bbb929c8-8fbe-4397-9dbb-9b2b20218538