Remove nav toggle and up-nav for desktop size screens

and remove breadcrumbs for the Studio docs, because these are
not needed when there's only one level of "tabs"

Also deleted a strangely redundant screen-size declaration for the header-tabs visiblity.

For now this applies only to Studio docs (body.studio selector).
Later, we should update the Android templates to use a new class
in the body such as "no-global-nav" to trigger these styles

Change-Id: If398814871980b56e3e0484244dee364198d687c