Validation: Remove ConnectTrace and PerBlockConnectTrace
ConnectTrace was introduced in 6fdd43b9
when the SyncTransactions signal needed to be fired outside the cs_main
scope. The CValidationInterface is now asynchronous and signals can be
fired while holding cs_main. Remove the ConnectTrace struct that needs
to be passed up and down the stack and just fire BlockConnected()
directly in ConnectTip().