If you’ve used Avast for a long time and have upgraded it to the most current version, you may have noticed avastSS.scr in your Windows directory. You can delete that file.
The current Avast uninstall utility does not remove that file, and the current version of Avast does not install that file.
It is a throw back to when avast had a screen saver scan, which has been removed in avast 17.x.xxxx.
I still have the avastSS.scr file, created on 28 November 2016, 18:57:15 on this win10 system. At just 51.9 KB in size I’m in no particular rush to remove it.
Just another example why I say to remove things manually 
It being there isn’t going to impact on anything, as the OP said.
“If you’ve used Avast for a long time and have upgraded it to the most current version, you may have noticed avastSS.scr in your Windows directory.”
I too have only updated from the UI on this win10 home 64bit laptop.
Program updates from the UI are going to be adding/modifying elements and not so much cleaning up. We can only hazard a guess if an uninstall and clean install would have removed it or not.