Remove deprecated Client::backend (#3951)

substrate/core/client/src/client.rs

@@ -342,15 +342,6 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 		self.backend.state_at(*block)
 	}
 
-	/// Expose backend reference. To be used in tests only
-	#[doc(hidden)]
-	#[deprecated(note="Rather than relying on `client` to provide this, access \
-	to the backend should be handled at setup only - see #1134. This function \
-	will be removed once that is in place.")]
-	pub fn backend(&self) -> &Arc<B> {
-		&self.backend
-	}
-
 	/// Given a `BlockId` and a key prefix, return the matching child storage keys in that block.
 	pub fn storage_keys(&self, id: &BlockId<Block>, key_prefix: &StorageKey) -> error::Result<Vec<StorageKey>> {
 		let keys = self.state_at(id)?.keys(&key_prefix.0).into_iter().map(StorageKey).collect();