Merge #14561: Remove fs::relative call and fix listwalletdir tests

Summary:
ed2e18398b3ab657e98e3e1fe135cbf8dd94fda3 Remove fs::relative call and fix listwalletdir tests (João Barbosa)

Pull request description:

The implementation of `fs::relative` resolves symlinks which is not intended
in ListWalletDir. The replacement does what is required, and `listwalletdir` RPC
tests are fixed accordingly.

Also, `fs::recursive_directory_iterator` iteration is fixed to build with boost 1.47.

Based on #14559

Tree-SHA512: 1da516226073f195285d10d9d9648c90cce0158c5d1eb9c31217bb4abb575cd37f07c00787c5a850554d6120bbc5a3cbc5cb47d4488b32ac6bcb52bc1882d600

Backport of Core PR14561

Depends on D5546

Test Plan:

ninja
test_runner.py wallet_multiwallet

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D5547