ConnectTrace used to subscribe to the mempool's NotifyEntryRemoved
callback to be notified of transactions removed for conflict. Since
PerBlockConnectTrace no longer tracks conflicted transactions,
ConnectTrace no longer requires these notifications.
This is a backport of Core PR17477 [4 & 5/6]
Backport note: these 2 commits have been squashed because the first one left an unused private attribute 'pool', causing a warning / error for build-clang
Depends on D8866