Update mempool and compact block logic to use TxHash
This allowed to catch a few erroneous uses of GetId when GetHash should have been used, so this is already a plus.
Depends on D4599
make check ./test/functional/test_runner.py
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D4600