refactor: remove unused screenchange variable

[ThomasFrans]

The screenchange member variable on Layout didn't seem to be used for anything except for debugging. A comment in on_layout makes it seem like it wasn't meant to be used for debugging purposes but for actual functionality that wasn't implemented.

[ThomasFrans]

Back with more insane space savings, a whole 1 byte this time 😝

I was adding some documentation to Layout and wondered what this variable was for so looked it up, and except for the debug line, I don't see what it does. I think it might have been for future functionality that was never implemented. If it was for debugging purposes only, it makes sense, but a comment mentioned it was also used to let views know the active focus view was changed, something I can't find an implementation for. I could be wrong.

I just thought I'd remove it to clean up the code and avoid confusion about what this variable is for.

[hrkfdn]

Indeed, looks like a leftover. Merged, thanks!