Simplify some pattern-matches (#16402) (#16446)

When those match an exact combinator on Option / Result.

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

(cherry picked from commit b08cff9e77)

Co-authored-by: François Garillot <4142+huitseeker@users.noreply.github.com>

ledger-tool/src/main.rs

@@ -1661,10 +1661,11 @@ fn main() {
                     let parse_results = {
                         if let Some(slot_string) = frozen_regex.captures_iter(&line).next() {
                             Some((slot_string, &mut frozen))
-                        } else if let Some(slot_string) = full_regex.captures_iter(&line).next() {
-                            Some((slot_string, &mut full))
                         } else {
-                            None
+                            full_regex
+                                .captures_iter(&line)
+                                .next()
+                                .map(|slot_string| (slot_string, &mut full))
                         }
                     };