The wallet now uses TransactionRemovedFromMempool to be notified about
conflicted wallet, and no other clients use vtxConflicted.
This is a backport of Core PR17477 [2/6]
https://github.com/bitcoin/bitcoin/pull/17477/commits/cdb893443cc16edf974f099b8485e04b3db1b1d7
Depends on D8864
See D6653 for differences in validationinterface.cpp