Use #[derive(Default)] instead of manually implementing it

compiler/rustc_lint/src/unused.rs

@@ -1023,6 +1023,7 @@ declare_lint! {
     "`if`, `match`, `while` and `return` do not need parentheses"
 }
 
+#[derive(Default)]
 pub(crate) struct UnusedParens {
     with_self_ty_parens: bool,
     /// `1 as (i32) < 2` parses to ExprKind::Lt
@@ -1030,12 +1031,6 @@ pub(crate) struct UnusedParens {
     parens_in_cast_in_lt: Vec<ast::NodeId>,
 }
 
-impl Default for UnusedParens {
-    fn default() -> Self {
-        Self { with_self_ty_parens: false, parens_in_cast_in_lt: Vec::new() }
-    }
-}
-
 impl_lint_pass!(UnusedParens => [UNUSED_PARENS]);
 
 impl UnusedDelimLint for UnusedParens {