Update mempool and compact block logic to use TxHash

Summary:
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

Test Plan:

make check
./test/functional/test_runner.py

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D4600