Use the plain Aes.Create() instead of Aes.Create("AesManaged")

[Numpsy]

refs #746, #664

There is no indication in the code as to why it explicitly requests the managed AES implementation rather than just using the default, and there are other places in the library that just use Aes.Create(), so this is an attempt at changing it to see if all the tests etc still work.

Also refs https://learn.microsoft.com/en-us/dotnet/api/system.security.cryptography.aes.create?view=net-7.0#system-security-cryptography-aes-create(system-string) which says that the version of Aes.Create that takes a string name has been obsoleted in .NET 7.0