### 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
if (default_renderer_mobile.is_empty()) {
		default_renderer_mobile = "gl_compatibility";
	}
	
	if (rendering_driver.is_empty() && rendering_method.is_empty() && project_manager) {
		rendering_driver = "opengl3";
		rendering_method = "gl_compatibility";
		default_renderer_mobile = "gl_compatibility";
	}
#endif
	if (renderer_hints.is_empty()) {
		ERR_PRINT("No renderers available.");
	}
	if (!rendering_method.is_empty()) {
		if (rendering_method != "forward_plus" &&
				rendering_method != "mobile" &&
				rendering_method != "gl_compatibility") {
			OS::get_singleton()->print("Unknown renderer name '%s', aborting. Valid options are: %s\n", rendering_method.utf8().get_data(), renderer_hints.utf8().get_data());
			goto error;
		}
	}
	if (!rendering_driver.is_empty()) {
		
		
		
		bool found = false;
		for (int i = 0; i < DisplayServer::get_create_function_count(); i++) {
			Vector<String> r_drivers = DisplayServer::get_create_function_rendering_drivers(i);
			for (int d = 0; d < r_drivers.size(); d++) {
				if (rendering_driver == r_drivers[d]) {