[backport#10973] Remove use of CRPCTable::appendCommand in wallet code

Summary:
4e4d9e9f85eaf9c3bec48559bd4cad3e8a9333ca This commit does not change behavior. (Russell Yanofsky)

Depends on D5871

This is a partial backport of Core PR10973

Test Plan:

export CC=clang CXX=clang++
cmake .. -GNinja -DCMAKE_BUILD_TYPE=Debug -DENABLE_SANITIZERS=undefined
ninja check check-functional

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D5906