x11: Simplify some more event-rewrite code.

ui/aura/window_tree_host.cc

Index: ui/aura/window_tree_host.cc
diff --git a/ui/aura/window_tree_host.cc b/ui/aura/window_tree_host.cc
index cefafb42524d30d24dae6601e60d0b2f3673bfdb..2f60c7c3a732431dd9074f2487e899d934474005 100644
--- a/ui/aura/window_tree_host.cc
+++ b/ui/aura/window_tree_host.cc
@@ -290,11 +290,6 @@ void WindowTreeHost::OnHostCloseRequested() {
                     OnHostCloseRequested(this));
 }
 
-void WindowTreeHost::OnKeyboardMappingChanged() {
-  FOR_EACH_OBSERVER(WindowTreeHostObserver, observers_,
-                    OnKeyboardMappingChanged(this));
-}
-
 void WindowTreeHost::MoveCursorToInternal(const gfx::Point& root_location,
                                           const gfx::Point& host_location) {
   MoveCursorToNative(host_location);