rust-clippy: simplify `match` to `if let`

This was hinted at by clippy, and makes it more obvious that nothing is
happening in the `None` case.

rust/rhg/src/commands/status.rs

@@ -446,8 +446,7 b' pub fn run(invocation: &crate::CliInvoca'
     };
     let (narrow_matcher, narrow_warnings) = narrow::matcher(repo)?;
 
-    match revpair {
-        Some((rev1, rev2)) => {
+    if let Some((rev1, rev2)) = revpair {
             let mut ds_status = DirstateStatus::default();
             if list_copies {
                 return Err(CommandError::unsupported(
@@ -493,8 +492,6 b' pub fn run(invocation: &crate::CliInvoca'
             output.output(display_states, ds_status)?;
             return Ok(());
         }
-        None => (),
-    }
 
     let (sparse_matcher, sparse_warnings) = sparse::matcher(repo)?;
     let matcher = match (repo.has_narrow(), repo.has_sparse()) {