Merge #10522: [wallet] Remove unused variables

Summary:
a8c09af Remove unused variables (practicalswift)

Tree-SHA512: 34807dc3a0471c83b086f430b66465602c8f6a3a158b54ace2ec8afb746f1f5907f7dfcde5a4bad4041df9721ec46b61681b2dbf89725c9c8c4c5ad0ca99f78f

Backport of Core PR10522
https://github.com/bitcoin/bitcoin/pull/10522/

Test Plan:

make check
test_runner.py

Reviewers: jasonbcox, deadalnix, Fabien, O1 Bitcoin ABC, #bitcoin_abc

Reviewed By: Fabien, O1 Bitcoin ABC, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D3247