[flutter_tools] delete flutter format command (#129360)

On the current stable branch (3.10.x), `flutter format` no longer works, and gives an error. This change just deletes the code.

Fixes flutter/flutter#115809

Author: christopherfujino

packages/flutter_tools/lib/executable.dart

@@ -28,7 +28,6 @@ import 'src/commands/doctor.dart';
 import 'src/commands/downgrade.dart';
 import 'src/commands/drive.dart';
 import 'src/commands/emulators.dart';
-import 'src/commands/format.dart';
 import 'src/commands/generate.dart';
 import 'src/commands/generate_localizations.dart';
 import 'src/commands/ide_config.dart';
@@ -200,7 +199,6 @@ List<FlutterCommand> generateCommands({
     signals: globals.signals,
   ),
   EmulatorsCommand(),
-  FormatCommand(),
   GenerateCommand(),
   GenerateLocalizationsCommand(
     fileSystem: globals.fs,