Seed legacy platform storage explicitly and drop Android app handles

src/app.h

@@ -155,10 +155,6 @@ public:
     int idle_ms = 100;
     pp::platform::PlatformServices* platform_services_ = nullptr;
     
-#ifdef __ANDROID__
-    struct android_app* and_app;
-    struct engine* and_engine;
-#endif
     std::string clipboard_get_text();
     bool clipboard_set_text(const std::string& s);
     void pick_image(std::function<void(std::string path)> callback);