Element destructor does not need to check pseudo elements or animations

At the time when the Element destructor runs the element should have
already been detached so we don't need to cancel animations or clear
pseudo elements (detach already did it).

Review URL: https://codereview.chromium.org/123683003

git-svn-id: svn://svn.chromium.org/blink/trunk@164698 bbb929c8-8fbe-4397-9dbb-9b2b20218538