### Godot version

master

### System information

Ubuntu

### Issue description

I think one of the recent changes wrapped the project converter in `#ifndef DISABLE_DEPRECATED` but missed the coresponding code in `main.cpp` (and potentially other places).
```
main/main.cpp: In static member function 'static bool Main::start()':
main/main.cpp:2551:33: error: 'ProjectConverter3To4' was not declared in this scope
 2551 |                 int exit_code = ProjectConverter3To4(converter_max_kb_file, converter_max_line_length).convert();
      |                                 ^~~~~~~~~~~~~~~~~~~~
main/main.cpp:2556:33: error: 'ProjectConverter3To4' was not declared in this scope
 2556 |                 int exit_code = ProjectConverter3To4(converter_max_kb_file, converter_max_line_length).validate_conversion();
```

### Steps to reproduce

for instance, try to compile with `deprecated = "no"` in your `custom.py`.

### Minimal reproduction project

n/a
static InputMap *input_map = nullptr;
static TranslationServer *translation_server = nullptr;
static Performance *performance = nullptr;
static PackedData *packed_data = nullptr;
static Time *time_singleton = nullptr;
#ifdef MINIZIP_ENABLED
static ZipArchive *zip_packed_data = nullptr;
#endif
static FileAccessNetworkClient *file_access_network_client = nullptr;
static MessageQueue *message_queue = nullptr;
static AudioServer *audio_server = nullptr;
static DisplayServer *display_server = nullptr;
static RenderingServer *rendering_server = nullptr;
static CameraServer *camera_server = nullptr;
static XRServer *xr_server = nullptr;
static TextServerManager *tsman = nullptr;
static PhysicsServer3DManager *physics_server_3d_manager = nullptr;
static PhysicsServer3D *physics_server_3d = nullptr;
static PhysicsServer2DManager *physics_server_2d_manager = nullptr;
static PhysicsServer2D *physics_server_2d = nullptr;
static NavigationServer3D *navigation_server_3d = nullptr;
static NavigationServer2D *navigation_server_2d = nullptr;
static ThemeDB *theme_db = nullptr;
static bool _start_success = false;
String tablet_driver = "";
String text_driver = "";
String rendering_driver = "";
String rendering_method = "";
static int text_driver_idx = -1;
static int display_driver_idx = -1;