refactor visit_type_expr_err_mut

Summary: as per title

Reviewed By: rajneesh

Differential Revision: D63901103

fbshipit-source-id: 3b1be0b6d16cde750b9badc592aa09b6633270fb

Author: perehonchuk

starlark_syntax/src/syntax/uniplate.rs

@@ -557,15 +557,12 @@ impl<P: AstPayload> ExprP<P> {
         &mut self,
         f: &mut impl FnMut(&mut AstTypeExprP<P>) -> Result<(), E>,
     ) -> Result<(), E> {
-        match self {
-            ExprP::Lambda(lambda) => {
-                for param in &mut lambda.params {
-                    if let (_, Some(ty), _) = param.split_mut() {
-                        f(ty)?;
-                    }
+        if let ExprP::Lambda(lambda) = self {
+            for param in &mut lambda.params {
+                if let (_, Some(ty), _) = param.split_mut() {
+                    f(ty)?;
                 }
             }
-            _ => {}
         }
         self.visit_expr_err_mut(|expr| expr.visit_type_expr_err_mut(f))
     }