Remove uses of the old plugin model from the analysis server

pkg/analysis_server/test/edit/postfix_completion_test.dart

Index: pkg/analysis_server/test/edit/postfix_completion_test.dart
diff --git a/pkg/analysis_server/test/edit/postfix_completion_test.dart b/pkg/analysis_server/test/edit/postfix_completion_test.dart
index 136b816f38f6313d843ee5b24167fa7f6960add7..61fb2f68d685c030208d174b09b92f9c2bb0cc27 100644
--- a/pkg/analysis_server/test/edit/postfix_completion_test.dart
+++ b/pkg/analysis_server/test/edit/postfix_completion_test.dart
@@ -6,7 +6,6 @@ import 'package:analysis_server/protocol/protocol.dart';
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analysis_server/src/edit/edit_domain.dart';
 import 'package:analyzer_plugin/protocol/protocol_common.dart';
-import 'package:plugin/manager.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
 
@@ -26,8 +25,6 @@ class PostfixCompletionTest extends AbstractAnalysisTest {
   void setUp() {
     super.setUp();
     createProject();
-    ExtensionManager manager = new ExtensionManager();
-    manager.processPlugins([server.serverPlugin]);
     handler = new EditDomainHandler(server);
   }