Remove subxt (#460)

* Remove subxt

Removes ~20 crates from our Cargo.lock.

Removes downloading the metadata and enables removing the getMetadata RPC route
(relevant to #379).

Moves forward #337.

Done now due to distinctions in the subxt 0.32 API surface which make it
justifiable to not update.

* fmt, update due to deny triggering on a yanked crate

* Correct the handling of substrate_block_notifier now that it's ephemeral, not long-lived

* Correct URL in tests/coordinator from ws to http

coordinator/src/main.rs

@@ -1222,8 +1222,8 @@ async fn main() {
 
   let serai = || async {
     loop {
-      let Ok(serai) = Serai::new(&format!(
-        "ws://{}:9944",
+      let Ok(serai) = Serai::new(format!(
+        "http://{}:9944",
         serai_env::var("SERAI_HOSTNAME").expect("Serai hostname wasn't provided")
       ))
       .await