Merge #13437: wallet: Erase wtxOrderd wtx pointer on removeprunedfunds

Summary:
faa18ca046e9043b2cf68cb1bd17cc8c60fe26d9 wallet: Erase wtxOrderd wtx pointer on removeprunedfunds (MarcoFalke)

Pull request description:

This prevents segfaults, when reading from the freed memory.

Tree-SHA512: 04f8190dea7901cf1cc298d5db98c83b02858f27114c5ef4da738accd176d6647d6b81f3dc39f3d5912b1a981cf0599370fd391c4154ffbde97afc1fac389123

Backport of Core PR13437
https://github.com/bitcoin/bitcoin/pull/13437/

Test Plan:

make check
test_runner.py

Reviewers: deadalnix, Fabien, jasonbcox, O1 Bitcoin ABC, #bitcoin_abc

Reviewed By: Fabien, O1 Bitcoin ABC, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D4540