[Accessibility] Invalid ARIA attributes in Discover "no results" prompt

[bhavyarm]

Kibana version: master

Browser version: chrome latest

Browser OS version: OS X

Original install method (e.g. download page, yum, from source, etc.): built from source

Description of the problem including expected versus actual behavior: I ran google accessibility audit on discover. One of the errors: "ARIA state and property values must be valid on discover" is on the following code snippet.

<a class="kuiButton kuiButton--primary kuiButton--small" ng-click="kbnTopNav.toggle('filter')" aria-expanded="kbnTopNav.is('filter')" aria-label="time picker" data-test-subj="discoverNoResultsTimefilter"><span aria-hidden="true" class="kuiIcon fa-clock-o"></span> time picker</a>

This link gives more information about the error.
https://github.com/GoogleChrome/accessibility-developer-tools/wiki/Audit-Rules#ax_aria_04