Fix lint errors

js/impress.js

@@ -2965,7 +2965,7 @@
                 // For example, when clicking on the button to launch speaker console, the button
                 // is immediately deleted from the DOM. In this case target is a DOM element when
                 // we get it, but turns out to be null if you try to actually do anything with it.
-                foo = target.id;
+                target.id;
             }
             catch(err) {
                 return;
@@ -2995,7 +2995,7 @@
         gc.addEventListener( document, "click", function( event ) {
             var target = event.target;
             try {
-                foo = target.id;
+                target.id; 
             }
             catch(err) {
                 return;