Only allow quickload from debug menu (CleverRaven#63767)

* Disable quickload in non-debug builds

Quickloading was never intended to be a non-debug feature, but by
enabling the keybind outside of debug builds, it was effectively made
so.
Fix that.

src/game.cpp

@@ -2408,7 +2408,9 @@ input_context get_default_mode_input_context()
     ctxt.register_action( "workout" );
     ctxt.register_action( "save" );
     ctxt.register_action( "quicksave" );
+#if !defined(RELEASE)
     ctxt.register_action( "quickload" );
+#endif
     ctxt.register_action( "SUICIDE" );
     ctxt.register_action( "player_data" );
     ctxt.register_action( "map" );