Always check if the Windows Defender is present/was removed. Since if Windows Defender is enabled (which it is by Microsoft Default) it can lead to serious performance and other issues on servers!
Personally I would like to see the Avast agent being so smart to detect a running Windows Defender and prevent installation of the Avast AV service or terminate the Avast installer at all with a nice message window.
The thing is that Avast installer is not able to remove Windows Defender as it can be found here: https://businesshelp.avast.com/Content/Products/AfB_Management_Consoles/DeviceManagement/RemovableAV.htm?_ga=2.186712360.1063210931.1720339934-1471763923.1672732140