base: simplification of redundant role=navigation
- Removes redundant role on nav. "In the majority of cases setting an ARIA role and/or aria-* attribute that matches the default implicit ARIA semantics is unnecessary and not recommended as these properties are already set by the browser". See: http://www.w3.org/TR/html5/dom.html#aria-usage-note and http://www.w3.org/TR/html5/sections.html#the-nav-element