message: remove explicit Default impl
diff: @@ -2,7 +2,7 @@ use crate::{DatabaseKeyIndex, RuntimeId};
  use rustc_hash::FxHashMap;
  use smallvec::SmallVec;
  -#[derive(Debug)]
  +#[derive(Debug, Default)]
  pub(super) struct DependencyGraph {
  /// A `(K -> V)` pair in this map indicates that the the runtime
  /// `K` is blocked on some query executing in the runtime `V`.
  @@ -21,15 +21,6 @@ struct Edge {
  path: Vec<DatabaseKeyIndex>,
  }
  -impl Default for DependencyGraph {
  - fn default() -> Self {
  - DependencyGraph {
  - edges: Default::default(),
  - query_dependents: Default::default(),
  - }
  - }
  -}
  -
  impl DependencyGraph {
  /// True if `from_id` depends on `to_id`.
  ///
  