SQL Server 2016 AlwaysOn VDI_CLIENT_WORKER command
After some more research I discovered that when I create an AG with autoseeding SQL Server creates a new worker (that executes the VDI_CLIENT_WORKER command) for each scheduler. 
To remove those workers I need remove every 'autoseeded' AG and restart the SQL Server service.

If I then create the AG with full backup/restore none of these workers are created.