Make apps with transparent backgrounds work on phones by making wallpaper not invisible for staged mode

I removed a line, that makes the wallpaper invisible, when an app is opened in staged mode (default mode on phones). I hope this can solve the issue with transparent apps like the terminal app (#85 (closed)).

Please be aware, that I do not know much about how Lomiri works and that I do not know, why this line was there before. I tested this solution on a Pixel 3a with Ubuntu Touch 20.04 and I did not encounter any problems.