tests: Remove unused testing code

Summary:
Removal of dead python code

Partial backport of PR14365
Commit https://github.com/bitcoin/bitcoin/pull/14365/commits/590a57fdecc2eb2e8208d82e491d09a1986e4f0e
Depends on D7981 (backported out of order)

Test Plan: ninja && ninja check-functional

Reviewers: O1 Bitcoin ABC, #bitcoin_abc, deadalnix

Reviewed By: O1 Bitcoin ABC, #bitcoin_abc, deadalnix

Subscribers: deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D7987