### 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
static int audio_driver_idx = -1;
static bool single_window = false;
static bool editor = false;
static bool project_manager = false;
static bool cmdline_tool = false;
static String locale;
static bool show_help = false;
static bool auto_quit = false;
static OS::ProcessID editor_pid = 0;
#ifdef TOOLS_ENABLED
static bool found_project = false;
static bool auto_build_solutions = false;
static String debug_server_uri;
static int converter_max_kb_file = 4 * 1024; 
static int converter_max_line_length = 100000;
HashMap<Main::CLIScope, Vector<String>> forwardable_cli_arguments;
#endif
bool use_startup_benchmark = false;
String startup_benchmark_file;
static DisplayServer::WindowMode window_mode = DisplayServer::WINDOW_MODE_WINDOWED;
static DisplayServer::ScreenOrientation window_orientation = DisplayServer::SCREEN_LANDSCAPE;
static DisplayServer::VSyncMode window_vsync_mode = DisplayServer::VSYNC_ENABLED;
static uint32_t window_flags = 0;
static Size2i window_size = Size2i(1152, 648);
static int init_screen = DisplayServer::SCREEN_PRIMARY;
static bool init_fullscreen = false;
static bool init_maximized = false;
static bool init_windowed = false;
static bool init_always_on_top = false;
static bool init_use_custom_pos = false;