Merge #10308: [wallet] Securely erase potentially sensitive keys/values

Summary:
6c914ac [wallet] Securely erase potentially sensitive keys/values (Thomas Snider)

Tree-SHA512: 071d88c4093108d4e4eced35a6ffcebe3f499798194f5b1be661ffa5b78b5f55311667f6d2a72758d85290f61f958381ee95d380b9045ca18e9e1875f0e686c8

Backport Core PR10308
https://github.com/bitcoin/bitcoin/pull/10308/files

Test Plan:

make check
test_runner.py

Reviewers: deadalnix, Fabien, #bitcoin_abc, markblundeberg

Reviewed By: #bitcoin_abc, markblundeberg

Subscribers: markblundeberg

Differential Revision: https://reviews.bitcoinabc.org/D3107