### 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
converting_project = true;
		} else if (args[i] == "--validate-conversion-3to4") {
			validating_converting_project = true;
		} else if (args[i] == "-e" || args[i] == "--editor") {
			editor = true;
		} else if (args[i] == "-p" || args[i] == "--project-manager") {
			project_manager = true;
#endif
		} else if (args[i].length() && args[i][0] != '-' && positional_arg.is_empty()) {
			positional_arg = args[i];
			if (args[i].ends_with(".scn") ||
					args[i].ends_with(".tscn") ||
					args[i].ends_with(".escn") ||
					args[i].ends_with(".res") ||
					args[i].ends_with(".tres")) {
				/
				/
				/
				/
				/
				/
				game_path = args[i];
			}
		}
		/
		else if (i < (args.size() - 1)) {
			bool parsed_pair = true;
			if (args[i] == "-s" || args[i] == "--script") {
				script = args[i + 1];
#ifdef TOOLS_ENABLED