Remove deprecated methods

[jamesramsden-bh]

Some methods have been marked with a todo to remove. Conversation with @tg359 confirmed that these can indeed be removed.

Remove these methods by adding the appropriate attributes. If a method has been replaced, then delete the old method, and add this attribute to the replacement one, e.g.

[PreviousVersion("6.3","BH.Engine.Python.Compute.IsValidEnvironmentName(System.String)")]

If the method is being removed without replacement, then we flag it for removal with the ToBeRemoved attribute, e.g.

[ToBeRemoved("6.3", "This method has been removed.")]