delete FlutterCommand.intArg(), which is not used anywhere in the codebase (#122124)

Delete `FlutterCommand.intArg()`, which is not used anywhere

Author: bartekpacia

packages/flutter_tools/lib/src/runner/flutter_command.dart

@@ -1734,9 +1734,6 @@ abstract class FlutterCommand extends Command<void> {
     return argResults![name] as String?;
   }
 
-  /// Gets the parsed command-line option named [name] as an `int`.
-  int? intArg(String name) => argResults?[name] as int?;
-
   /// Gets the parsed command-line option named [name] as `List<String>`.
   List<String> stringsArg(String name) {
     return argResults![name]! as List<String>? ?? <String>[];