HTMLInputElement does not need to call confusingAndOftenMisusedAttached()

There's no reason to manually manage the attached state like it was doing.

Review URL: https://codereview.chromium.org/48743006

git-svn-id: svn://svn.chromium.org/blink/trunk@160756 bbb929c8-8fbe-4397-9dbb-9b2b20218538