refactor(iroh, iroh-blobs, iroh-net)!: remove deprecated items (#2652)

## Description

Removes items deprecated in the last release.

## Breaking Changes

### iroh-blobs
- `iroh_blobs::store::fs::Store::import_flat_store` was previously
deprecated and is now removed. Use iroh <= `0.22.0` to migrate.
- `iroh_blobs::store::fs::FlatStorePaths` is removed. This was only used
for importing flat stores, which were previously deprecated. Use iroh <=
`0.22.0` to migrate.

### iroh
- Automatic migration from flat stores is no longer possible. This was
previously deprecated. Use iroh <= `0.22.0` to migrate.

### iroh-net
- `iroh_net::endpoint::RemoteInfo::last_alive_relay` was previously
deprecated and it's now removed.

## Notes & open questions

n/a

## Change checklist

- [x] Self-review.
- [ ] ~~Documentation updates following the [style
guide](https://rust-lang.github.io/rfcs/1574-more-api-documentation-conventions.html#appendix-a-full-conventions-text),
if relevant.~~
- [x] Tests if relevant.
- [x] All breaking changes documented.

iroh-blobs/src/store/fs.rs

@@ -86,7 +86,6 @@ use smallvec::SmallVec;
 use tokio::io::AsyncWriteExt;
 use tracing::trace_span;
 
-mod import_flat_store;
 mod migrate_redb_v1_v2;
 mod tables;
 #[doc(hidden)]
@@ -586,11 +585,6 @@ pub(crate) enum ActorMessage {
         cmd: Export,
         tx: oneshot::Sender<ActorResult<()>>,
     },
-    /// Modification method: import an entire flat store into the redb store.
-    ImportFlatStore {
-        paths: FlatStorePaths,
-        tx: oneshot::Sender<bool>,
-    },
     /// Update inline options
     UpdateInlineOptions {
         /// The new inline options
@@ -680,8 +674,7 @@ impl ActorMessage {
             Self::UpdateInlineOptions { .. }
             | Self::Sync { .. }
             | Self::Shutdown { .. }
-            | Self::Fsck { .. }
-            | Self::ImportFlatStore { .. } => MessageCategory::TopLevel,
+            | Self::Fsck { .. } => MessageCategory::TopLevel,
             #[cfg(test)]
             Self::EntryState { .. } => MessageCategory::ReadOnly,
         }
@@ -698,17 +691,6 @@ enum MessageCategory {
 pub(crate) type FilterPredicate<K, V> =
     Box<dyn Fn(u64, AccessGuard<K>, AccessGuard<V>) -> Option<(K, V)> + Send + Sync>;
 
-/// Parameters for importing from a flat store
-#[derive(Debug)]
-pub struct FlatStorePaths {
-    /// Complete data files
-    pub complete: PathBuf,
-    /// Partial data files
-    pub partial: PathBuf,
-    /// Metadata files such as the tags table
-    pub meta: PathBuf,
-}
-
 /// Storage that is using a redb database for small files and files for
 /// large files.
 #[derive(Debug, Clone)]
@@ -756,15 +738,6 @@ impl Store {
     pub async fn dump(&self) -> io::Result<()> {
         Ok(self.0.dump().await?)
     }
-
-    /// Import from a v0 or v1 flat store, for backwards compatibility.
-    #[deprecated(
-        since = "0.23.0",
-        note = "Flat stores are deprecated and future versions will not be able to migrate."
-    )]
-    pub async fn import_flat_store(&self, paths: FlatStorePaths) -> io::Result<bool> {
-        Ok(self.0.import_flat_store(paths).await?)
-    }
 }
 
 #[derive(Debug)]
@@ -1001,14 +974,6 @@ impl StoreInner {
         Ok(rx.await??)
     }
 
-    async fn import_flat_store(&self, paths: FlatStorePaths) -> OuterResult<bool> {
-        let (tx, rx) = oneshot::channel();
-        self.tx
-            .send(ActorMessage::ImportFlatStore { paths, tx })
-            .await?;
-        Ok(rx.await?)
-    }
-
     async fn update_inline_options(
         &self,
         inline_options: InlineOptions,
@@ -2193,10 +2158,6 @@ impl ActorState {
 
     fn handle_toplevel(&mut self, db: &redb::Database, msg: ActorMessage) -> ActorResult<()> {
         match msg {
-            ActorMessage::ImportFlatStore { paths, tx } => {
-                let res = self.import_flat_store(db, paths);
-                tx.send(res?).ok();
-            }
             ActorMessage::UpdateInlineOptions {
                 inline_options,
                 reapply,