### 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
#endif
	OS::get_singleton()->print("  --remote-debug <uri>              Remote debug (<protocol>://<host/IP>[:<port>], e.g. tcp://127.0.0.1:6007).\n");
#if defined(DEBUG_ENABLED)
	OS::get_singleton()->print("  --debug-collisions                Show collision shapes when running the scene.\n");
	OS::get_singleton()->print("  --debug-paths                     Show path lines when running the scene.\n");
	OS::get_singleton()->print("  --debug-navigation                Show navigation polygons when running the scene.\n");
	OS::get_singleton()->print("  --debug-stringnames               Print all StringName allocations to stdout when the engine quits.\n");
#endif
	OS::get_singleton()->print("  --frame-delay <ms>                Simulate high CPU load (delay each frame by <ms> milliseconds).\n");
	OS::get_singleton()->print("  --time-scale <scale>              Force time scale (higher values are faster, 1.0 is normal speed).\n");
	OS::get_singleton()->print("  --disable-vsync                   Forces disabling of vertical synchronization, even if enabled in the project settings. Does not override driver-level V-Sync enforcement.\n");
	OS::get_singleton()->print("  --disable-render-loop             Disable render loop so rendering only occurs when called explicitly from script.\n");
	OS::get_singleton()->print("  --disable-crash-handler           Disable crash handler when supported by the platform code.\n");
	OS::get_singleton()->print("  --fixed-fps <fps>                 Force a fixed number of frames per second. This setting disables real-time synchronization.\n");
	OS::get_singleton()->print("  --print-fps                       Print the frames per second to the stdout.\n");
	OS::get_singleton()->print("\n");
	OS::get_singleton()->print("Standalone tools:\n");
	OS::get_singleton()->print("  -s, --script <script>             Run a script.\n");
	OS::get_singleton()->print("  --check-only                      Only parse for errors and quit (use with --script).\n");
#ifdef TOOLS_ENABLED
	OS::get_singleton()->print("  --export-release <preset> <path>  Export the project in release mode using the given preset and output path. The preset name should match one defined in export_presets.cfg.\n");
	OS::get_singleton()->print("                                    <path> should be absolute or relative to the project directory, and include the filename for the binary (e.g. 'builds/game.exe').\n");
	OS::get_singleton()->print("                                    The target directory must exist.\n");
	OS::get_singleton()->print("  --export-debug <preset> <path>    Export the project in debug mode using the given preset and output path. See --export-release description for other considerations.\n");
	OS::get_singleton()->print("  --export-pack <preset> <path>     Export the project data only using the given preset and output path. The <path> extension determines whether it will be in PCK or ZIP format.\n");
	OS::get_singleton()->print("  --convert-3to4 [<max_file_kb>] [<max_line_size>]\n");
	OS::get_singleton()->print("                                    Converts project from Godot 3.x to Godot 4.x.\n");
	OS::get_singleton()->print("  --validate-conversion-3to4 [<max_file_kb>] [<max_line_size>]\n");
	OS::get_singleton()->print("                                    Shows what elements will be renamed when converting project from Godot 3.x to Godot 4.x.\n");
	OS::get_singleton()->print("  --doctool [<path>]                Dump the engine API reference to the given <path> (defaults to current dir) in XML format, merging if existing files are found.\n");