### 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
} else if (I->get() == "--dump-gdextension-interface") {
			
			editor = true;
			cmdline_tool = true;
			dump_gdextension_interface = true;
			print_line("Dumping GDExtension interface header file");
			
			
			
			main_args.push_back(I->get());
		} else if (I->get() == "--dump-extension-api") {
			
			editor = true;
			cmdline_tool = true;
			dump_extension_api = true;
			print_line("Dumping Extension API");
			
			
			
			main_args.push_back(I->get());
		} else if (I->get() == "--export-release" || I->get() == "--export-debug" ||
				I->get() == "--export-pack") { 
			
			editor = true;
			cmdline_tool = true;
			main_args.push_back(I->get());
		} else if (I->get() == "--convert-3to4") {
			
			cmdline_tool = true;
			main_args.push_back(I->get());