Remove uses of cs_main in wallet code

Summary:
This commit does not change behavior.

Partial backport of core PR14437:
https://github.com/bitcoin/bitcoin/pull/14437/commits/79d579f4e11b57f90fed314bccd25230f918729f

Depends on D5063 and D5074.

Test Plan:

cmake -GNinja .. -DCMAKE_BUILD_TYPE=Debug
ninja check check-functional

Run the CI TSAN build configuration.

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D5075