Remove unnecessary getters and setters from botbuilder libraries

[axelsrz]

Since the getters and setters don't have any validation or additional logic baked in, having these are a little superfluous. It's more pythonic to not use the @property and @property_name.setter unless necessary.

As we spoke irl, there are a couple of other data model classes in the libraries that should be updated as well to just have public attributes instead of these getters and setters.

Originally posted by @stevengum in https://github.com/microsoft/botbuilder-python/diffs