`CBlockPolicyEstimator` will implement `CValidationInterface` and
subscribe to its notification to process transactions added and removed
from the mempool.
Re-delegate calculation of `validForFeeEstimation` from validation to fee estimator.
Also clean up the validForFeeEstimation arg thats no longer needed in `CTxMempool`.
Co-authored-by: Matt Corallo <git@bluematt.me>
With subpackage evaluation and de-duplication, it's not always the
entire package that is used in CheckFeerate. To be more helpful to the
caller, specify which transactions were included in the evaluation and
what the feerate was.
Instead of PCKG_POLICY (which is supposed to be for package-wide
errors), use PCKG_TX.
