[backport#15288] Remove use of IsInitialBlockDownload in wallet code

Summary:
a1df1b48a80bf122efa73677ff72577ec0103a3b This commit does not change behavior. (Russell Yanofksi)

Depends on D5868, completes T602

This is a backport of Core PR15288

Test Plan:

cmake .. -GNinja -DENABLE_WERROR=ON -DCMAKE_BUILD_TYPE=Debug
ninja check

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D5869