### 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
OS::get_singleton()->print("  -l, --language <locale>           Use a specific locale (<locale> being a two-letter code).\n");
	OS::get_singleton()->print("  --path <directory>                Path to a project (<directory> must contain a 'project.godot' file).\n");
	OS::get_singleton()->print("  -u, --upwards                     Scan folders upwards for project.godot file.\n");
	OS::get_singleton()->print("  --main-pack <file>                Path to a pack (.pck) file to load.\n");
	OS::get_singleton()->print("  --render-thread <mode>            Render thread mode ['unsafe', 'safe', 'separate'].\n");
	OS::get_singleton()->print("  --remote-fs <address>             Remote filesystem (<host/IP>[:<port>] address).\n");
	OS::get_singleton()->print("  --remote-fs-password <password>   Password for remote filesystem.\n");
	OS::get_singleton()->print("  --audio-driver <driver>           Audio driver [");
	for (int i = 0; i < AudioDriverManager::get_driver_count(); i++) {
		if (i > 0) {
			OS::get_singleton()->print(", ");
		}
		OS::get_singleton()->print("'%s'", AudioDriverManager::get_driver(i)->get_name());
	}
	OS::get_singleton()->print("].\n");
	OS::get_singleton()->print("  --display-driver <driver>         Display driver (and rendering driver) [");
	for (int i = 0; i < DisplayServer::get_create_function_count(); i++) {
		if (i > 0) {
			OS::get_singleton()->print(", ");
		}
		OS::get_singleton()->print("'%s' (", DisplayServer::get_create_function_name(i));
		Vector<String> rd = DisplayServer::get_create_function_rendering_drivers(i);
		for (int j = 0; j < rd.size(); j++) {
			if (j > 0) {
				OS::get_singleton()->print(", ");
			}
			OS::get_singleton()->print("'%s'", rd[j].utf8().get_data());
		}
		OS::get_singleton()->print(")");
	}