Fix lint warnings and cleanup unused code after RadioGroup migration

Remove unused imports, fields, variables, and dead code introduced
during the RadioGroup widget migration and prior changes.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

test/services/localization_service_test.dart

@@ -62,7 +62,6 @@ void main() {
           data = json.decode(content) as Map<String, dynamic>;
         } catch (e) {
           fail('$name is not valid JSON: $e');
-          return; // unreachable, keeps analyzer happy
         }
         expect(
           data['language'],

test/services/network_status_test.dart

@@ -1,5 +1,5 @@
 import 'package:flutter_test/flutter_test.dart';
-import '../../lib/services/network_status.dart';
+import 'package:deflockapp/services/network_status.dart';
 
 void main() {
   group('NetworkStatus', () {