### 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
RenderingServer::get_singleton()->is_render_loop_enabled()) {
		if ((!force_redraw_requested) && OS::get_singleton()->is_in_low_processor_usage_mode()) {
			if (RenderingServer::get_singleton()->has_changed()) {
				RenderingServer::get_singleton()->draw(true, scaled_step); /
				Engine::get_singleton()->frames_drawn++;
			}
		} else {
			RenderingServer::get_singleton()->draw(true, scaled_step); /
			Engine::get_singleton()->frames_drawn++;
			force_redraw_requested = false;
		}
	}
	process_ticks = OS::get_singleton()->get_ticks_usec() - process_begin;
	process_max = MAX(process_ticks, process_max);
	uint64_t frame_time = OS::get_singleton()->get_ticks_usec() - ticks;
	for (int i = 0; i < ScriptServer::get_language_count(); i++) {
		ScriptServer::get_language(i)->frame();
	}
	AudioServer::get_singleton()->update();
	if (EngineDebugger::is_active()) {
		EngineDebugger::get_singleton()->iteration(frame_time, process_ticks, physics_process_ticks, physics_step);
	}
	frames++;
	Engine::get_singleton()->_process_frames++;
	if (frame > 1000000) {
		/
		if (hide_print_fps_attempts == 0) {
			if (editor || project_manager) {
				if (print_fps) {
					print_line(vformat("Editor FPS: %d (%s mspf)", frames, rtos(1000.0 / frames).pad_decimals(2)));