Trim Win32 runtime and VR retained state

src/platform_windows/windows_runtime_shell.cpp

@@ -24,7 +24,6 @@ struct RetainedMainWindowSessionState final {
 
 struct RetainedWindowsRuntimeState final {
     std::unique_ptr<App> owned_app;
-    App* app = nullptr;
     WacomTablet tablet;
 };
 
@@ -131,20 +130,18 @@ void shutdown_main_window_runtime(const MainWindowStartupState& startup, HINSTAN
 
 void bind_app(App* app) noexcept
 {
-    retained_runtime_state().app = app;
     App::I = app;
 }
 
 App* bound_app() noexcept
 {
-    return retained_runtime_state().app;
+    return App::I;
 }
 
 void release_bound_app() noexcept
 {
-    auto& state = retained_runtime_state();
     bind_app(nullptr);
-    state.owned_app.reset();
+    retained_runtime_state().owned_app.reset();
 }
 
 WacomTablet* bound_wacom_tablet() noexcept