Fix erroneous restoration of task model state.

pkg/analyzer/test/generated/incremental_resolver_test.dart

Index: pkg/analyzer/test/generated/incremental_resolver_test.dart
diff --git a/pkg/analyzer/test/generated/incremental_resolver_test.dart b/pkg/analyzer/test/generated/incremental_resolver_test.dart
index 5457524925dad3979ba9511b46530e33cbb7cb47..dd9394ce1e666717abb62df45ba8ef33c570e333 100644
--- a/pkg/analyzer/test/generated/incremental_resolver_test.dart
+++ b/pkg/analyzer/test/generated/incremental_resolver_test.dart
@@ -3521,17 +3521,10 @@ class A {
 
   @override
   void setUp() {
-    AnalysisEngine.instance.useTaskModel = true;
     super.setUp();
     _resetWithIncremental(true);
   }
 
-  @override
-  void tearDown() {
-    super.tearDown();
-    AnalysisEngine.instance.useTaskModel = false;
-  }
-
   void test_computeConstants() {
     _resolveUnit(r'''
 int f() => 0;