chore(deps): update bdk_wallet version

- delete version pin
- explicitly bump to 2.4.0

2.4.0 ships a fix for the deprecated marking on part of the code,
so we bump to it explicitly to make the requirement visible.

We don't revert the pin commit because Cargo.lock still locks 2.1.0,
so a plain revert wouldn't be enough to get rid of the deprecated
errors.

Author: va-an

Cargo.lock

@@ -12,7 +12,7 @@ readme = "README.md"
 license = "MIT"
 
 [dependencies]
-bdk_wallet = { version = "=2.1.0", features = ["rusqlite", "keys-bip39", "compiler", "std"] }
+bdk_wallet = { version = "2.4.0", features = ["rusqlite", "keys-bip39", "compiler", "std"] }
 clap = { version = "4.6", features = ["derive","env"] }
 clap_complete = "4.6"
 dirs = {  version = "6.0.0" }