Remove the unused class SingleContextManager

pkg/analysis_server/test/test_all.dart

Index: pkg/analysis_server/test/test_all.dart
diff --git a/pkg/analysis_server/test/test_all.dart b/pkg/analysis_server/test/test_all.dart
index 9edc74f0c05da3f5cd04dbe0116bb0573e079d93..dc66f8405fe49bd81e08eee67d63f8688d983f90 100644
--- a/pkg/analysis_server/test/test_all.dart
+++ b/pkg/analysis_server/test/test_all.dart
@@ -21,7 +21,6 @@ import 'protocol_server_test.dart' as protocol_server_test;
 import 'protocol_test.dart' as protocol_test;
 import 'search/test_all.dart' as search_all;
 import 'services/test_all.dart' as services_all;
-import 'single_context_manager_test.dart' as single_context_manager_test;
 import 'socket_server_test.dart' as socket_server_test;
 import 'source/test_all.dart' as source_all;
 import 'src/test_all.dart' as src_all;
@@ -48,7 +47,6 @@ main() {
     protocol_test.main();
     search_all.main();
     services_all.main();
-    single_context_manager_test.main();
     socket_server_test.main();
     source_all.main();
     src_all.main();