Remove the old task model

pkg/analyzer/lib/src/task/dart_work_manager.dart

Index: pkg/analyzer/lib/src/task/dart_work_manager.dart
diff --git a/pkg/analyzer/lib/src/task/dart_work_manager.dart b/pkg/analyzer/lib/src/task/dart_work_manager.dart
index 793d9ce4f22336643f3e0182dac9856dbb0d7ce5..a586b3b4c65b81504a9b11fd5b968ac45479b4a9 100644
--- a/pkg/analyzer/lib/src/task/dart_work_manager.dart
+++ b/pkg/analyzer/lib/src/task/dart_work_manager.dart
@@ -474,7 +474,7 @@ class DartWorkManager implements WorkManager {
   }
 
   bool _shouldErrorsBeComputed(Source source) =>
-      context.shouldErrorsBeAnalyzed(source, null);
+      context.shouldErrorsBeAnalyzed(source);
 
   static bool _isDartSource(AnalysisTarget target) {
     return target is Source && AnalysisEngine.isDartFileName(target.fullName);