Unfortunately there isn’t a simple Yes, No answer as there are many sub-folders within the Windows folder and there are also many files within the windows sub-folder structure that actually aren’t ‘windows’ a.k.a. Microsoft/system files. So it would only apply to contents in this avast sub-folder.

As for ensuring other AV remnants are gone:

Antivirus Remover is a handy application that will bring you the uninstallation program for any of the supported security software listed in the main window.
Requires .NET Framework 4.0

Re Windows Defender (WD):
This shouldn’t be a problem if you aren’t using windows 8.0 or 8.1 as that version is essentially Microsoft Security Essentials re-badged as WD. So for other OSes not an issue, but it brings very little to the party, so most would disable it in windows 7 as it can’t be installed. For earlier OS versions I think that WD has to be downloaded and installed, in which case I would suggest uninstalling it.