don't change controller visibility on keyboard input

- We do want to set it to visible in case it's hidden
- We don't want to set it to 'hidden' because then hover commands can't
  bring it back to visible state (e.g. YouTube player)

Fixes https://github.com/igrigorik/videospeed/issues/91.

inject.js

@@ -242,9 +242,6 @@ chrome.extension.sendMessage({}, function(response) {
           iterations: 1,
           delay: 0
         });
-        controllerAnimation.onfinish = function(e) {
-          controller.style.visibility = 'hidden';
-        }
       }
     });
   }