My first guess would be that the warnings arise because of the non-standard repositories, in your case, the
wine repositories at the bottom of the list.
To test the theory, you can comment out all the lines containing winehq by adding a comment sign (a hashmark) to front of each of these lines. You can try the
apt update command afterwards. If the warnings don’t reappear, we found the problem. So those lines should look like this:
#deb http://dl.winehq.org/wine-builds/ubuntu/ artful main
#deb-src http://dl.winehq.org/wine-builds/ubuntu/ artful main
#deb https://dl.winehq.org/wine-builds/ubuntu/ disco main
#deb-src https://dl.winehq.org/wine-builds/ubuntu/ disco main
By doing so you disable these software sources. You can enable them later.
You can edit the file with a text editor, like
vi from the terminal, like this:
$ sudo vi /etc/apt/sources.list
If you are not familiar yet with that editor, we have a vim tutorial to get you started.
Note: if you use the “preformatted text” in your post editor on this forum’s interface when you copy-paste, the markings do not get interpreted as commands by the forum engine, thus making such a configuration file’s contents more readable.