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

substrate/client/tests/burn.rs

@@ -94,7 +94,7 @@ serai_test!(
           &pair,
           &SeraiCoins::burn_with_instruction(instruction.clone()),
           0,
-          Default::default(),
+          0,
         )
     )
     .await;