ElementShadow::detach does need to check confusingAndOftenMisusedAttached()

If the ElementShadow is going through a detach (meaning its in the Document)
then all the ShadowRoots are attached as well so there's no reason to check.
This is the same as ContainerNode::detachChildren which also doesn't check.

Review URL: https://codereview.chromium.org/48593006

git-svn-id: svn://svn.chromium.org/blink/trunk@160871 bbb929c8-8fbe-4397-9dbb-9b2b20218538