Unify window fullscreen and minimizing implementation

ui/views/mus/desktop_window_tree_host_mus.h

Index: ui/views/mus/desktop_window_tree_host_mus.h
diff --git a/ui/views/mus/desktop_window_tree_host_mus.h b/ui/views/mus/desktop_window_tree_host_mus.h
index 85ccf6996863dc9625191fdcf5e0695cfc15c45b..fa074ba085883e24b996da65efe61ed20afd4fc0 100644
--- a/ui/views/mus/desktop_window_tree_host_mus.h
+++ b/ui/views/mus/desktop_window_tree_host_mus.h
@@ -143,10 +143,6 @@ class VIEWS_MUS_EXPORT DesktopWindowTreeHostMus
 
   DesktopNativeWidgetAura* desktop_native_widget_aura_;
 
-  // State to restore window to when exiting fullscreen. Only valid if
-  // fullscreen.
-  ui::WindowShowState fullscreen_restore_state_;
-
   // We can optionally have a parent which can order us to close, or own
   // children who we're responsible for closing when we CloseNow().
   DesktopWindowTreeHostMus* parent_ = nullptr;