[chain_redesign] Remove old structures

Other changes:

* The `async-https` feature of `bdk_esplora` is no longer default.
* Rename `ObservedAs` to `ChainPosition`.
* Set temporary MSRV to 1.60.0 to compile all workspace members will all
  features.

crates/file_store/src/lib.rs

@@ -1,16 +1,10 @@
 #![doc = include_str!("../README.md")]
 mod entry_iter;
-mod keychain_store;
 mod store;
 use std::io;
 
-use bdk_chain::{
-    keychain::{KeychainChangeSet, KeychainTracker, PersistBackend},
-    sparse_chain::ChainPosition,
-};
 use bincode::{DefaultOptions, Options};
 pub use entry_iter::*;
-pub use keychain_store::*;
 pub use store::*;
 
 pub(crate) fn bincode_options() -> impl bincode::Options {
@@ -46,28 +40,3 @@ impl<'a> From<io::Error> for FileError<'a> {
 }
 
 impl<'a> std::error::Error for FileError<'a> {}
-
-impl<K, P> PersistBackend<K, P> for KeychainStore<K, P>
-where
-    K: Ord + Clone + core::fmt::Debug,
-    P: ChainPosition,
-    KeychainChangeSet<K, P>: serde::Serialize + serde::de::DeserializeOwned,
-{
-    type WriteError = std::io::Error;
-
-    type LoadError = IterError;
-
-    fn append_changeset(
-        &mut self,
-        changeset: &KeychainChangeSet<K, P>,
-    ) -> Result<(), Self::WriteError> {
-        KeychainStore::append_changeset(self, changeset)
-    }
-
-    fn load_into_keychain_tracker(
-        &mut self,
-        tracker: &mut KeychainTracker<K, P>,
-    ) -> Result<(), Self::LoadError> {
-        KeychainStore::load_into_keychain_tracker(self, tracker)
-    }
-}