Revert "Browser: Allow system shortcuts to function"

This reverts commit 2e8ff1855c.

We had some awkward timing around the merging of this commit and commit
b073fdd570. With both commits in tree, we
are now processing hotkey activations twice. For example, ctrl+t will
open 2 tabs.

Userland/Applications/Browser/BrowserWindow.cpp

@@ -718,10 +718,6 @@ void BrowserWindow::event(Core::Event& event)
     case GUI::Event::Resize:
         broadcast_window_size(static_cast<GUI::ResizeEvent&>(event).size());
         break;
-    case GUI::Event::KeyDown:
-        // FIXME: add support for hotkeys *within* ladybird
-        event.ignore();
-        break;
     default:
         break;
     }