Elements. Remove elementModelDeprecationMsg. It is no longer used.

Change-Id: I54c2262f834d63ebaaccdac7fac6e51c934a017f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/425140
Reviewed-by: Paul Berry <[email protected]>
Commit-Queue: Konstantin Shcheglov <[email protected]>

Author: scheglov

pkg/analyzer/lib/src/dart/element/element.dart

@@ -59,11 +59,6 @@ import 'package:analyzer/src/utilities/extensions/string.dart';
 import 'package:collection/collection.dart';
 import 'package:pub_semver/pub_semver.dart';
 
-const String elementModelDeprecationMsg = '''
-This is part of the old analyzer element model. Please see
-https://github.com/dart-lang/sdk/blob/main/pkg/analyzer/doc/element_model_migration_guide.md
-for information about how to migrate to the new element model.''';
-
 @Deprecated('Do not use implementation classes')
 // TODO(scheglov): https://github.com/dart-lang/dartdoc/issues/4039
 typedef ConstructorElementImpl = ConstructorFragmentImpl;