trivial: Improve include comment in src/interfaces/wallet.h
trivial: Improve include comment in src/interfaces/wallet.h

Summary:
Backport of Bitcoin Core PR13026
https://github.com/bitcoin/bitcoin/pull/13026

Test Plan:
```
make check
```

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

Reviewed By: Fabien, O1 Bitcoin ABC, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D3930

cculianu/bitcoin-abc,cculianu/bitcoin-abc,ftrader-bitcoinabc/bitcoin-abc,ftrader-bitcoinabc/bitcoin-abc,ftrader-bitcoinabc/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,cculianu/bitcoin-abc,ftrader-bitcoinabc/bitcoin-abc,ftrader-bitcoinabc/bitcoin-abc,cculianu/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,ftrader-bitcoinabc/bitcoin-abc,cculianu/bitcoin-abc,ftrader-bitcoinabc/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,ftrader-bitcoinabc/bitcoin-abc,cculianu/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,ftrader-bitcoinabc/bitcoin-abc,cculianu/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,ftrader-bitcoinabc/bitcoin-abc,Bitcoin-ABC/bitcoin-abc,cculianu/bitcoin-abc,Bitcoin-ABC/bitcoin-abc