window: rebase hide-back-button

android system has solved back problem, set back button again.

src/anbox/platform/sdl/window.cpp

@@ -40,7 +40,6 @@ namespace platform {
 namespace sdl {
 Window::Id Window::Invalid{-1};
 const std::map<std::string, Window::window_property> Window::property_map = {
-  {"QQ音乐", Window::HIDE_BACK},
   {"喜马拉雅", Window::HIDE_MAXIMIZE},
   {"i深圳", Window::HIDE_MAXIMIZE}
 };