Simplify some pattern-matches (#16402)

When those match an exact combinator on Option / Result.

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

core/src/cluster_slots.rs

@@ -191,8 +191,7 @@ impl ClusterSlots {
             .read()
             .unwrap()
             .keys()
-            .filter(|x| **x > root)
-            .filter(|x| !my_slots.contains(*x))
+            .filter(|x| **x > root && !my_slots.contains(*x))
             .map(|x| RepairType::HighestShred(*x, 0))
             .collect()
     }

core/src/crds.rs

@@ -747,8 +747,10 @@ mod test {
                 let num_epoch_slots = crds
                     .table
                     .values()
-                    .filter(|value| value.insert_timestamp >= since)
-                    .filter(|value| matches!(value.value.data, CrdsData::EpochSlots(_, _)))
+                    .filter(|value| {
+                        value.insert_timestamp >= since
+                            && matches!(value.value.data, CrdsData::EpochSlots(_, _))
+                    })
                     .count();
                 assert_eq!(num_epoch_slots, crds.get_epoch_slots_since(since).count());
                 for value in crds.get_epoch_slots_since(since) {

core/src/duplicate_shred.rs

@@ -226,10 +226,7 @@ pub fn into_shreds(
         chunk_index,
         chunk,
         ..
-    } = match chunks.next() {
-        None => return Err(Error::InvalidDuplicateShreds),
-        Some(chunk) => chunk,
-    };
+    } = chunks.next().ok_or(Error::InvalidDuplicateShreds)?;
     let slot_leader = leader(slot).ok_or(Error::UnknownSlotLeader)?;
     let check_chunk = check_chunk(slot, shred_index, shred_type, num_chunks);
     let mut data = HashMap::new();

core/src/rpc.rs

@@ -3185,16 +3185,14 @@ pub mod rpc_full {
             let address = verify_pubkey(address)?;
 
             let config = config.unwrap_or_default();
-            let before = if let Some(before) = config.before {
-                Some(verify_signature(&before)?)
-            } else {
-                None
-            };
-            let until = if let Some(until) = config.until {
-                Some(verify_signature(&until)?)
-            } else {
-                None
-            };
+            let before = config
+                .before
+                .map(|ref before| verify_signature(before))
+                .transpose()?;
+            let until = config
+                .until
+                .map(|ref until| verify_signature(until))
+                .transpose()?;
             let limit = config
                 .limit
                 .unwrap_or(MAX_GET_CONFIRMED_SIGNATURES_FOR_ADDRESS2_LIMIT);