### 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
#endif
	if (init_windowed) {
		
	} else if (init_maximized) {
		DisplayServer::get_singleton()->window_set_mode(DisplayServer::WINDOW_MODE_MAXIMIZED);
	} else if (init_fullscreen) {
		DisplayServer::get_singleton()->window_set_mode(DisplayServer::WINDOW_MODE_FULLSCREEN);
	}
	if (init_always_on_top) {
		DisplayServer::get_singleton()->window_set_flag(DisplayServer::WINDOW_FLAG_ALWAYS_ON_TOP, true);
	}
	MAIN_PRINT("Main: Load Boot Image");
	Color clear = GLOBAL_DEF_BASIC("rendering/environment/defaults/default_clear_color", Color(0.3, 0.3, 0.3));
	RenderingServer::get_singleton()->set_default_clear_color(clear);
	if (show_logo) { 
		const bool boot_logo_image = GLOBAL_DEF_BASIC("application/boot_splash/show_image", true);
		const String boot_logo_path = String(GLOBAL_DEF_BASIC(PropertyInfo(Variant::STRING, "application/boot_splash/image", PROPERTY_HINT_FILE, "*.png"), String())).strip_edges();
		const bool boot_logo_scale = GLOBAL_DEF_BASIC("application/boot_splash/fullsize", true);
		const bool boot_logo_filter = GLOBAL_DEF_BASIC("application/boot_splash/use_filter", true);
		Ref<Image> boot_logo;
		if (boot_logo_image) {
			if (!boot_logo_path.is_empty()) {
				boot_logo.instantiate();
				Error load_err = ImageLoader::load_image(boot_logo_path, boot_logo);
				if (load_err) {
					ERR_PRINT("Non-existing or invalid boot splash at '" + boot_logo_path + "'. Loading default splash.");
				}
			}
		} else {