Clean up of library examples.
Deleted Arduino_Due_CAN_Sample_1 as duplicate of EchoTest
Deleted Arduino_Due_CAN_Sample_2 as using features specific to Due
Deleted Arduino_Due_CAN_Sample_3 as using features specific to Due
Deleted Arduino_Due_CAN_Sample_4 and rolled functionality into ExtendedPingPong
Deleted CAN_Data_Logging as Due specific and functionally the same as ReceiveCANMessages
Deleted CAN_EchoTest as Due specific and functionally the same as
  a combination of ReceiveCANMessages & SendCANMessages
Deleted CAN_TrafficSnooper as Due specific and functionally the same as ReceiveCANMessages