### 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
bool upwards = false;
	String debug_uri = "";
	bool skip_breakpoints = false;
	String main_pack;
	bool quiet_stdout = false;
	int rtm = -1;
	String remotefs;
	String remotefs_pass;
	Vector<String> breakpoints;
	bool use_custom_res = true;
	bool force_res = false;
	String default_renderer = "";
	String default_renderer_mobile = "";
	String renderer_hints = "";
	packed_data = PackedData::get_singleton();
	if (!packed_data) {
		packed_data = memnew(PackedData);
	}
#ifdef MINIZIP_ENABLED
	
	zip_packed_data = ZipArchive::get_singleton();
	
	if (!zip_packed_data) {
		zip_packed_data = memnew(ZipArchive);
	}
	packed_data->add_pack_source(zip_packed_data);
#endif
	
	Error exit_code = ERR_INVALID_PARAMETER;
	I = args.front();