The only CValidationInterface client that cares about transactions that
are removed from the mempool because of CONFLICT is the wallet.Start using the TransactionRemovedFromMempool method to notify about
conflicted transactions instead of using the vtxConflicted vector in
BlockConnected.
This is a backport of Core PR17477 [1/6]
https://github.com/bitcoin/bitcoin/pull/17477/commits/1168394d759b13af68acec6d5bfa04aaa24561f8