message: remove unused memo function
diff: @@ -30,11 +30,6 @@ impl<V> MemoMap<V> {
  self.map.insert(key, ArcSwap::from(Arc::new(memo)));
  }
  - /// Removes any existing memo for the given key.
  - pub(super) fn remove(&self, key: DerivedKeyIndex) {
  - self.map.remove(&key);
  - }
  -
  /// Evicts the existing memo for the given key, replacing it
  /// with an equivalent memo that has no value. If the memo
  /// has untracked inputs, this has no effect.
  