[chronik] Fix a bug upon tx invalidation

Summary:
When a tx is invalidated due to a conflict, it causes chronik to fail with a double spend error when the invlidation event occurs.
It's time to properly implement the probe_tx function so it doesn't collide with the mempool anymore.

Test Plan:

./test/functional/test_runner.py chronik_*

Reviewers: #bitcoin_abc, tobias_ruck

Reviewed By: #bitcoin_abc, tobias_ruck

Subscribers: tobias_ruck

Differential Revision: https://reviews.bitcoinabc.org/D18542