mem: Remove Packet source from ForwardResponseRecord
mem: Remove Packet source from ForwardResponseRecord

This patch removes the source field from the ForwardResponseRecord,
but keeps the class as it is part of how the cache identifies
responses to hardware prefetches that are snooped upwards.
(transplanted from 3a3bb559b112e95143461d97a7d4bbf2e02c639a)

andrewfu0325/gem5-aladdin,andrewfu0325/gem5-aladdin,andrewfu0325/gem5-aladdin,andrewfu0325/gem5-aladdin,andrewfu0325/gem5-aladdin,andrewfu0325/gem5-aladdin,andrewfu0325/gem5-aladdin