"Fixes" the delete by Primary Key(s) on the DynamoDB Helper Class

It does this by doing some very awful reflection magic that assumes that the given input class is annotated with at least DynamoDBHashKey and DynamoDBRangeKey (if required).

It's extremely clunky and only done as a proof-of-concept. I think in general this should be abandoned and the deleteByPrimaryKey should be deprecated.