Remove obsolete document wrapper creation in named constructors

For historical reasons, named constructor callbacks contained the code

  toV8(document, info.Holder(), isolate);

to ensure a document wrapper was created. This was necessary to ensure
the asynchronous lifetime of HTMLAudioElement and HTMLImageElement.

This is no longer the case, so drop the extra code.

R=haraken
BUG=

Review URL: https://codereview.chromium.org/353623003

git-svn-id: svn://svn.chromium.org/blink/trunk@176868 bbb929c8-8fbe-4397-9dbb-9b2b20218538