[whatwg] Drop tabindex=""

[ddailey]

Simon Pieters writes:

The "tab order" should be up to the user. In Opera you can navigate in
any direction you want using e.g. Shift+arrows, allowing you to freely
navigate in tables for instance. The author shouldn't have any say about
the tab order other than the source order.


In a table, I think I agree. The user should know how to get around via UI 
conventions.
In more abstract structures, the author may be able to provide useful hints 
through tab order.

DD