### 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
display_driver = NULL_DISPLAY_DRIVER;
			main_args.push_back(I->get());
#endif
		} else if (I->get() == "--path") { // set path of project to start or edit
			if (I->next()) {
				String p = I->next()->get();
				if (OS::get_singleton()->set_cwd(p) != OK) {
					OS::get_singleton()->print("Invalid project path specified: \"%s\", aborting.\n", p.utf8().get_data());
					goto error;
				}
				N = I->next()->next();
			} else {
				OS::get_singleton()->print("Missing relative or absolute path, aborting.\n");
				goto error;
			}
		} else if (I->get() == "-u" || I->get() == "--upwards") { 
			upwards = true;
		} else if (I->get() == "--quit") { 
			auto_quit = true;
		} else if (I->get().ends_with("project.godot")) {
			String path;
			String file = I->get();
			int sep = MAX(file.rfind("/"), file.rfind("\\"));
			if (sep == -1) {
				path = ".";
			} else {
				path = file.substr(0, sep);
			}
			if (OS::get_singleton()->set_cwd(path) == OK) {