Fix computation of errors to not run extra tasks

pkg/analyzer/lib/src/plugin/engine_plugin.dart

Index: pkg/analyzer/lib/src/plugin/engine_plugin.dart
diff --git a/pkg/analyzer/lib/src/plugin/engine_plugin.dart b/pkg/analyzer/lib/src/plugin/engine_plugin.dart
index 75debaaee30f385eca2d2e6dd35677bec3701acc..6c1e7031c75113a6cb2b47c1ac39c787e4ab64aa 100644
--- a/pkg/analyzer/lib/src/plugin/engine_plugin.dart
+++ b/pkg/analyzer/lib/src/plugin/engine_plugin.dart
@@ -159,8 +159,6 @@ class EnginePlugin implements Plugin {
 
   void _registerDartErrorsForSource(RegisterExtension registerExtension) {
     String id = DART_ERRORS_FOR_SOURCE_EXTENSION_POINT_ID;
-    registerExtension(id, BUILD_DIRECTIVES_ERRORS);
-    registerExtension(id, BUILD_LIBRARY_ERRORS);
     registerExtension(id, PARSE_ERRORS);
     registerExtension(id, SCAN_ERRORS);
   }