Remove aria-orientation="vertical" from sidebar wrapper div

[lhenze]

A11y issue -- automated audit --

Elements must only use supported ARIA attributes.

Impact: Critical

https://www.w3.org/WAI/WCAG22/Understanding/name-role-value.html

In the vertical sidebar for copyright, etc, one of the wrapper divs has
aria-orientation="vertical"
but it should not, because that's not a valid attribute for a div without a role.

Proposed solution: Remove that attribute from that div.