Remove logo role from header

The logo role doesn't exist.

themes/bootstrap3/templates/header.phtml

@@ -4,7 +4,7 @@
     <span class="sr-only">Toggle navigation</span>
     <i class="fa fa-bars"></i>
   </button>
-  <a role="logo" class="navbar-brand lang-<?=$this->layout()->userLang ?>" href="<?=$this->url('home')?>">VuFind</a>
+  <a class="navbar-brand lang-<?=$this->layout()->userLang ?>" href="<?=$this->url('home')?>">VuFind</a>
 </div>
 <? if ($this->layout()->searchbox !== false): ?>
   <section class="visible-lg">