Remove unused variables and/or function calls

Summary:
Backport 4-of-6 was skipped because the file was deleted in bitcoin-abc

This diff covers backport 5-of-6 for Core PR10781
https://github.com/bitcoin/bitcoin/pull/10781/commits/2e6080bbf31d5cc2e38e8a7b436e8ce1857e589b
T473
Depends on D2151

Test Plan:
test_runner.py
test_runner.py p2p-fullblocktest
test_runner.py bip68-sequence
test_runner.py fundrawtransaction

Reviewers: deadalnix, Fabien, #bitcoin_abc

Reviewed By: deadalnix, Fabien, #bitcoin_abc

Subscribers: teamcity

Differential Revision: https://reviews.bitcoinabc.org/D2166