Delete the migration tool

Change-Id: I40db4f08e5e440c336d512fa010ac2a2991575e9
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/336181
Reviewed-by: Samuel Rawlins <srawlins@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>

pkg/analysis_server/test/verify_sorted_test.dart

@@ -31,10 +31,6 @@ void main() {
   group('linter', () {
     buildTestsForLinter();
   });
-
-  group('nnbd_migration', () {
-    buildTestsForNnbdMigration();
-  });
 }
 
 void buildTests({
@@ -67,7 +63,6 @@ void buildTestsForAnalysisServer() {
     //  remove these exclusions.
     'lib/protocol/protocol_constants.dart',
     'lib/protocol/protocol_generated.dart',
-    'lib/src/edit/nnbd_migration/resources/resources.g.dart',
     'test/integration/support/integration_test_methods.dart',
     'test/integration/support/protocol_matchers.dart',
     // The following are not generated, but can't be sorted because they contain
@@ -124,12 +119,6 @@ void buildTestsForLinter() {
   ]);
 }
 
-void buildTestsForNnbdMigration() {
-  buildTests(
-      packagePath: 'nnbd_migration',
-      excludedPaths: ['lib/src/front_end/resources/resources.g.dart']);
-}
-
 void buildTestsIn(AnalysisSession session, String testDirPath,
     List<String> excludedPath, Folder directory) {
   var pathContext = session.resourceProvider.pathContext;