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/client/api/src/notifications.rs

@@ -51,19 +51,18 @@ impl StorageChangeSet {
 			.map(move |(k,v)| (None, k, v.as_ref()));
 		let children = self.child_changes
 			.iter()
-			.filter_map(move |(sk, changes)| {
-				if let Some(cf) = self.child_filters.as_ref() {
-					if let Some(filter) = cf.get(sk) {
-						Some(changes
+			.filter_map(move |(sk, changes)| 
+				self.child_filters.as_ref().and_then(|cf|
+					cf.get(sk).map(|filter| changes
 							.iter()
 							.filter(move |&(key, _)| match filter {
 								Some(ref filter) => filter.contains(key),
 								None => true,
 							})
-							.map(move |(k,v)| (Some(sk), k, v.as_ref())))
-					} else { None }
-				} else { None	}
-			})
+							.map(move |(k,v)| (Some(sk), k, v.as_ref()))
+					)
+				)
+			)
 			.flatten();
 		top.chain(children)
 	}