Define ss58 prefix inside the runtime (#7810)

* Add SS58Prefix type to the frame_system config trait

* Remove unused chain_id runtime interface

substrate/primitives/state-machine/src/basic.rs

@@ -263,8 +263,6 @@ impl Externalities for BasicExternalities {
 		crate::ext::StorageAppend::new(current).append(value);
 	}
 
-	fn chain_id(&self) -> u64 { 42 }
-
 	fn storage_root(&mut self) -> Vec<u8> {
 		let mut top = self.inner.top.clone();
 		let prefixed_keys: Vec<_> = self.inner.children_default.iter().map(|(_k, v)| {

substrate/primitives/state-machine/src/ext.rs

@@ -507,10 +507,6 @@ where
 		StorageAppend::new(current_value).append(value);
 	}
 
-	fn chain_id(&self) -> u64 {
-		42
-	}
-
 	fn storage_root(&mut self) -> Vec<u8> {
 		let _guard = guard();
 		if let Some(ref root) = self.storage_transaction_cache.transaction_storage_root {

substrate/primitives/state-machine/src/read_only.rs

@@ -156,8 +156,6 @@ impl<'a, H: Hasher, B: 'a + Backend<H>> Externalities for ReadOnlyExternalities<
 		unimplemented!("storage_append is not supported in ReadOnlyExternalities")
 	}
 
-	fn chain_id(&self) -> u64 { 42 }
-
 	fn storage_root(&mut self) -> Vec<u8> {
 		unimplemented!("storage_root is not supported in ReadOnlyExternalities")
 	}