Simple Exchange Sample does not need createEncryptionKey

[davidchesnut]

The Simple Exchange Sample has two methods in the Authentication class; createEncryptionKey and getEncryptionKey. They create and store an encryption key which is apparently never used. I recommend removing these methods as they make the Authentication class appear more complex than it actually is.

[marcote]

@davechmsft The Authentication class is simply a Helper class to ease developers the interaction with the ADAL library. In older and more complex examples we used to use mentioned methods. I will review if we can remove them.

[marcote]

We removed this functionality this code. Users should refer to ADAL if they want to handle this scenario.