Moved database to new server, not sure about NT AUTHORITY\* users
These users are built in accounts to Windows and they're usually hidden from view. If you know that your application isn't using those users then you can delete them.

However, it sounds like you're moving a database that was used in ASP.Net applications. ASP.Net does use both those accounts under the hood. NT AUTHORITY\IUSR for anonymous access and 
NT AUTHORITY\NETWORK SERVICE is used in ASP.Net application pools. If that's the case, make sure that you no longer need to access the database you moved with ASP.Net and you'll be golden.

http://www.iis.net/learn/get-started/planning-for-security/understanding-built-in-user-and-group-accounts-in-iis

https://msdn.microsoft.com/en-us/library/ff647402.aspx