[2.x] remove potential LogicException from translation methods

[jrushlow]

The VerifyEmailSignatureComponents $generatedAt property is always an int - we no longer need to throw a LogicException if the value is null in:

• getExpirationMessageKey()
• getExpirationMessageData()
• getExpiresAtIntervalInstance()

Consumers of this class do not need surround these methods with a try/catch(\LogicException) block.