[backport#15288] Remove uses of InitMessage/Warning/Error in wallet code

Summary:
e2c8ba9f6e782e2545b71e9e34b967c69e18c7f0 This commit does not change behavior. (Russell Yanofsky)

Depends on D5854

This is a partial backport of Core PR15288

Test Plan:

cmake .. -GNinja -DENABLE_WERROR=ON -DCMAKE_BUILD_TYPE=Debug -DBUILD_BITCOIN_WALLET=OFF
ninja check-all
cmake .. -GNinja -DENABLE_WERROR=ON -DCMAKE_BUILD_TYPE=Debug
ninja check-all

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D5858