Revert 156737 "Implement Custom Elements class-side inheritance."

This patch seems to causes crashes to some layout tests.

http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Win7%20%28dbg%29/builds/400

> Implement Custom Elements class-side inheritance.
> 
> DOM elements and ES6 do something called "class-side inheritance"
> where not only does an instance of subtype B's prototype point to base
> type A's prototype, the B constructor's prototype is A's
> constructor. This means that B.FOO works where FOO is a static
> operation or const attribute (in the WebIDL sense) of A.
> 
> This is described in this proposal:
> <https://www.w3.org/Bugs/Public/show_bug.cgi?id=22920>
> 
> BUG=271466
> 
> Review URL: https://chromiumcodereview.appspot.com/23386003

TBR=dominicc@chromium.org

Review URL: https://codereview.chromium.org/23498008

git-svn-id: svn://svn.chromium.org/blink/trunk@156785 bbb929c8-8fbe-4397-9dbb-9b2b20218538