### 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()->_writing_movie = true;
			} else {
				OS::get_singleton()->print("Missing write-movie argument, aborting.\n");
				goto error;
			}
		} else if (I->get() == "--disable-vsync") {
			disable_vsync = true;
		} else if (I->get() == "--print-fps") {
			print_fps = true;
		} else if (I->get() == "--profile-gpu") {
			profile_gpu = true;
		} else if (I->get() == "--disable-crash-handler") {
			OS::get_singleton()->disable_crash_handler();
		} else if (I->get() == "--skip-breakpoints") {
			skip_breakpoints = true;
		} else if (I->get() == "--xr-mode") {
			if (I->next()) {
				String xr_mode = I->next()->get().to_lower();
				N = I->next()->next();
				if (xr_mode == "default") {
					XRServer::set_xr_mode(XRServer::XRMODE_DEFAULT);
				} else if (xr_mode == "off") {
					XRServer::set_xr_mode(XRServer::XRMODE_OFF);
				} else if (xr_mode == "on") {
					XRServer::set_xr_mode(XRServer::XRMODE_ON);
				} else {
					OS::get_singleton()->print("Unknown --xr-mode argument \"%s\", aborting.\n", xr_mode.ascii().get_data());
					goto error;
				}
			} else {