kitty: 0.16.0 -> 0.17.1

https://github.com/kovidgoyal/kitty/releases/tag/v0.17.1

The png2icns patch is no longer needed because kitty will now automatically use `png2icns` when `iconutil` cannot be found.
The zsh completions will now work without needing to invoke them with `source`, which means, that we can just install them like the other shell completions.