Remove the singleton instance get/delete methods from RootWindow (yay)

ui/aura/root_window_host_linux.h

Index: ui/aura/root_window_host_linux.h
===================================================================
--- ui/aura/root_window_host_linux.h	(revision 124527)
+++ ui/aura/root_window_host_linux.h	(working copy)
@@ -17,8 +17,7 @@
 
 namespace aura {
 
-class RootWindowHostLinux : public RootWindowHost,
-                            public MessageLoop::DestructionObserver {
+class RootWindowHostLinux : public RootWindowHost {
  public:
   explicit RootWindowHostLinux(const gfx::Rect& bounds);
   virtual ~RootWindowHostLinux();
@@ -45,9 +44,6 @@
   virtual void MoveCursorTo(const gfx::Point& location) OVERRIDE;
   virtual void PostNativeEvent(const base::NativeEvent& event) OVERRIDE;
 
-  // MessageLoop::DestructionObserver Overrides.
-  virtual void WillDestroyCurrentMessageLoop() OVERRIDE;
-
   // Returns true if there's an X window manager present... in most cases.  Some
   // window managers (notably, ion3) don't implement enough of ICCCM for us to
   // detect that they're there.