Simplify some Option / Result / ? operator patterns (#8653)

* Simplify some Option / Result / ? operator patterns

When those match a combinator exactly.

Tool-aided by [comby-rust](https://github.com/huitseeker/comby-rust).

* adjust after review

* adjust post-review

substrate/utils/frame/rpc/system/src/lib.rs

@@ -207,10 +207,7 @@ where
 		let call_data = account.encode();
 		let future_best_header = future_best_header
 			.and_then(move |maybe_best_header| ready(
-				match maybe_best_header {
-					Some(best_header) => Ok(best_header),
-					None => Err(ClientError::UnknownBlock(format!("{}", best_hash))),
-				}
+				maybe_best_header.ok_or_else(|| { ClientError::UnknownBlock(format!("{}", best_hash)) })
 			));
 		let future_nonce = future_best_header.and_then(move |best_header|
 			fetcher.remote_call(RemoteCallRequest {

substrate/utils/frame/try-runtime/cli/src/lib.rs

@@ -169,10 +169,8 @@ impl TryRuntimeCmd {
 					uri: url.into(),
 					state_snapshot: snapshot_path.as_ref().map(SnapshotConfig::new),
 					modules: modules.clone().unwrap_or_default(),
-					at: match block_at {
-						Some(b) => Some(b.parse().map_err(|e| format!("Could not parse hash: {:?}", e))?),
-						None => None,
-					},
+					at: block_at.as_ref()
+						.map(|b| b.parse().map_err(|e| format!("Could not parse hash: {:?}", e))).transpose()?,
 					..Default::default()
 				})),
 			};