Updated score API: emit null when value is not present, remove updated timestamp.

app/lib/scorecard/backend.dart

@@ -210,12 +210,7 @@ class ScoreCardBackend {
       throw NotFoundException.resource('package "$package" version "$version"');
     }
 
-    var updated = pkg.updated;
     final card = await scoreCardBackend.getScoreCardData(package, v);
-    if (updated == null || card.updated?.isAfter(updated) == true) {
-      updated = card.updated;
-    }
-
     final tags = <String>{
       ...pkg.getTags(),
       ...pv.getTags(),
@@ -229,7 +224,6 @@ class ScoreCardBackend {
       downloadCount30Days:
           downloadCountsBackend.lookup30DaysTotalCounts(package),
       tags: tags.toList(),
-      lastUpdated: updated,
     );
   }
 }

app/test/frontend/handlers/custom_api_test.dart

@@ -180,8 +180,8 @@ void main() {
           'grantedPoints': greaterThan(10),
           'maxPoints': greaterThan(50),
           'likeCount': 0,
+          'downloadCount30Days': null,
           'tags': contains('sdk:dart'),
-          'lastUpdated': isNotEmpty,
         });
       },
     );

app/test/package/api_export/api_exporter_test.dart

@@ -155,8 +155,8 @@ Future<void> _testExportedApiSynchronization(
         'grantedPoints': isNotNull,
         'maxPoints': isNotNull,
         'likeCount': isNotNull,
+        'downloadCount30Days': null,
         'tags': isNotEmpty,
-        'lastUpdated': isNotNull,
       },
     );
     expect(

pkg/_pub_shared/lib/data/package_api.dart

@@ -274,22 +274,20 @@ class VersionInfo {
   Map<String, dynamic> toJson() => _$VersionInfoToJson(this);
 }
 
-@JsonSerializable(includeIfNull: false)
+@JsonSerializable(includeIfNull: true)
 class VersionScore {
   final int? grantedPoints;
   final int? maxPoints;
   final int? likeCount;
   final int? downloadCount30Days;
   final List<String>? tags;
-  final DateTime? lastUpdated;
 
   VersionScore({
     required this.grantedPoints,
     required this.maxPoints,
     required this.likeCount,
     required this.downloadCount30Days,
     required this.tags,
-    required this.lastUpdated,
   });
 
   factory VersionScore.fromJson(Map<String, dynamic> json) =>