Click on your Desktop and then press shift+command+G to open the Go To Folder dialog. Enter the following:
/Library/StagedExtensions/Applications
and then click GO.
A new Finder window will open inside the above path and anything that suggests it is an Avast or AVG-related item can be dragged and dropped to the Trash. Expect a password prompt to do this and supply your administrator password. Do not remove the /Library/StagedExtensions folder as it is installed by macOS.
No viruses are to be found on the Mac outside of laboratory circumstances so installing any anti-virus program is a waste of time and introduces other factors that can compromise your Mac's performance or false alarms about legitimate files. The operating system ships with its own built-in security anyway.
Malware and adware are potentially installable on your Mac and usually through downloads from application aggregation or Torrent sites. Only download from original vendor sites to avoid this issue. For these types of infections, anti-virus products cannot prevent them, and the free Malwarebytes application can detect and remove malware. No subscription is necessary, and Malwarebytes can be uninstalled from its Help menu.