### 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
return iterating > 0;
}
/
static uint64_t physics_process_max = 0;
static uint64_t process_max = 0;
static uint64_t navigation_process_max = 0;
bool Main::iteration() {
	/
	/
	iterating++;
	const uint64_t ticks = OS::get_singleton()->get_ticks_usec();
	Engine::get_singleton()->_frame_ticks = ticks;
	main_timer_sync.set_cpu_ticks_usec(ticks);
	main_timer_sync.set_fixed_fps(fixed_fps);
	const uint64_t ticks_elapsed = ticks - last_ticks;
	const int physics_ticks_per_second = Engine::get_singleton()->get_physics_ticks_per_second();
	const double physics_step = 1.0 / physics_ticks_per_second;