docs: remove PersistBackend from docs, Cargo.toml and wallet README.md

crates/file_store/Cargo.toml

@@ -5,7 +5,7 @@ edition = "2021"
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/bitcoindevkit/bdk"
 documentation = "https://docs.rs/bdk_file_store"
-description = "A simple append-only flat file implementation of PersistBackend for Bitcoin Dev Kit."
+description = "A simple append-only flat file database for persisting bdk_chain data."
 keywords = ["bitcoin", "persist", "persistence", "bdk", "file"]
 authors = ["Bitcoin Dev Kit Developers"]
 readme = "README.md"