Fine. Remove InstanceItemDuplicateItem. It is no longer used.

Change-Id: I1b17a21ca4991fc1a3fd852eaf0f88bf7996c076
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/425081
Commit-Queue: Konstantin Shcheglov <[email protected]>
Reviewed-by: Paul Berry <[email protected]>

Author: scheglov

pkg/analyzer/lib/src/fine/manifest_item.dart

@@ -112,53 +112,6 @@ sealed class InstanceItem<E extends InstanceElementImpl2>
   }
 }
 
-/// Placeholder for a name that has duplicate declared member.
-/// It is always given a new ID.
-class InstanceItemDuplicateItem
-    extends InstanceItemMemberItem<ExecutableElementImpl2> {
-  factory InstanceItemDuplicateItem() {
-    return InstanceItemDuplicateItem._(
-      id: ManifestItemId.generate(),
-      metadata: ManifestMetadata(annotations: []),
-      isStatic: false,
-    );
-  }
-
-  factory InstanceItemDuplicateItem.read(SummaryDataReader reader) {
-    return InstanceItemDuplicateItem._(
-      id: ManifestItemId.read(reader),
-      metadata: ManifestMetadata.read(reader),
-      isStatic: reader.readBool(),
-    );
-  }
-
-  InstanceItemDuplicateItem._({
-    required super.id,
-    required super.metadata,
-    required super.isStatic,
-  });
-
-  @override
-  bool match(MatchContext context, ExecutableElementImpl2 element) {
-    super.match(context, element); // we ignore it
-    // Duplicate items don't have any specific information, they are just
-    // a flag, that previously the same name was declared twice. So, there is
-    // no way to meaningfully match them. We always return `false`, and
-    // build a new item (and ID) for this name.
-    //
-    // The reason is that we don't want to prefer first or last duplicated
-    // element, we just wait until there is no error. And once it is fixed,
-    // we will build the actual item, with a new ID, and recompute all uses
-    // once again.
-    return false;
-  }
-
-  @override
-  void writeKind(BufferedSink sink) {
-    sink.writeEnum(_InstanceItemMemberItemKind.duplicate);
-  }
-}
-
 class InstanceItemGetterItem extends InstanceItemMemberItem<GetterElementImpl> {
   final ManifestType returnType;
   final ManifestNode? constInitializer;
@@ -251,8 +204,6 @@ sealed class InstanceItemMemberItem<E extends ExecutableElementImpl2>
   ) {
     var kind = reader.readEnum(_InstanceItemMemberItemKind.values);
     switch (kind) {
-      case _InstanceItemMemberItemKind.duplicate:
-        return InstanceItemDuplicateItem.read(reader);
       case _InstanceItemMemberItemKind.getter:
         return InstanceItemGetterItem.read(reader);
       case _InstanceItemMemberItemKind.method:
@@ -797,13 +748,7 @@ class TopLevelSetterItem extends TopLevelItem<SetterElementImpl> {
   }
 }
 
-enum _InstanceItemMemberItemKind {
-  duplicate,
-  constructor,
-  method,
-  getter,
-  setter,
-}
+enum _InstanceItemMemberItemKind { constructor, method, getter, setter }
 
 enum _ManifestItemKind {
   class_,