Bug 692295 - Remove nsWindowsShellService's ShortcutMaintenance method and calls now that it is no longer needed. r=jimm

Removes nsIWindowsShellService.idl since there are no longer custom methods and it can just use nsIShellService.idl
Removes a couple of includes that are no longer used and should have been removed after the code to delete Firefox prefetch files was removed

browser/components/shell/nsWindowsShellService.h

@@ -8,13 +8,12 @@
 
 #include "nscore.h"
 #include "nsString.h"
-#include "nsIWindowsShellService.h"
-#include "nsITimer.h"
+#include "nsIShellService.h"
 
 #include <windows.h>
 #include <ole2.h>
 
-class nsWindowsShellService : public nsIWindowsShellService
+class nsWindowsShellService : public nsIShellService
 {
   virtual ~nsWindowsShellService();
 
@@ -23,7 +22,6 @@ public:
 
   NS_DECL_ISUPPORTS
   NS_DECL_NSISHELLSERVICE
-  NS_DECL_NSIWINDOWSSHELLSERVICE
 
 protected:
   nsresult LaunchControlPanelDefaultsSelectionUI();