### 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
doc_tool_path = ".";
		}
#endif
	}
	uint64_t minimum_time_msec = GLOBAL_DEF(PropertyInfo(Variant::INT, "application/boot_splash/minimum_display_time", PROPERTY_HINT_RANGE, "0,100,1,or_greater,suffix:ms"), 0);
#ifdef TOOLS_ENABLED
	if (!doc_tool_path.is_empty()) {
		/
		Engine::get_singleton()->set_editor_hint(true);
		/
		if (!locale.is_empty() && locale != "en") {
			load_doc_translations(locale);
		}
		{
			Ref<DirAccess> da = DirAccess::open(doc_tool_path);
			ERR_FAIL_COND_V_MSG(da.is_null(), false, "Argument supplied to --doctool must be a valid directory path.");
		}
#ifndef MODULE_MONO_ENABLED
		/
		/
		/
		GLOBAL_DEF("dotnet/project/assembly_name", "");
		GLOBAL_DEF("dotnet/project/solution_directory", "");
#endif
		Error err;
		DocTools doc;
		doc.generate(doc_base);
		DocTools docsrc;
		HashMap<String, String> doc_data_classes;
		HashSet<String> checked_paths;