Deprecate nanoFramework nugets, remove code

[angularsen]

#1643 (comment)

@angularsen done! Check the repo here: nanoframework/nanoFramework.UnitsNet "initial" package published: nuget.org/packages/nanoFramework.UnitsNet.AbsorbedDoseOfIonizingRadiation (etc).

Now that it is moved to separate repo, we'll clean up on our end.

• Deprecate nanoFramework nugets
• Remove code