Merge bitcoindevkit/bdk#1785: test(wallet): small cleanups to test_wallet_transaction...

63465361ac524cc9af16b5a1b092bf5457a07f87 test(wallet): small cleanups to test_wallet_transactions_relevant (Steve Myers)

Pull request description:

  ### Description

  This cleans up the `test_wallet_transactions_relevant` test based on suggestions that didn't make it into #1779.

  ### Notes to the reviewers

  Also included a small use cleanup in wallet/mod.

  ### Changelog notice

  None.

  ### Checklists

  #### All Submissions:

  * [x] I've signed all my commits
  * [x] I followed the [contribution guidelines](https://github.com/bitcoindevkit/bdk/blob/master/CONTRIBUTING.md)
  * [x] I ran `cargo fmt` and `cargo clippy` before committing

ACKs for top commit:
  luisschwab:
    ACK 63465361ac524cc9af16b5a1b092bf5457a07f87
  ValuedMammal:
    ACK 63465361ac524cc9af16b5a1b092bf5457a07f87

Tree-SHA512: f9604518d2b9bb5614385a053efb03d53311f359626d45270f3648209ab0e31ba966995f842fff1c35f0c83848c61f0976f91524a3f457c6cd85e3f0929f4a77