### 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
OS::get_singleton()->print("].\n");
	OS::get_singleton()->print("  --rendering-method <renderer>     Renderer name. Requires driver support.\n");
	OS::get_singleton()->print("  --rendering-driver <driver>       Rendering driver (depends on display driver).\n");
	OS::get_singleton()->print("  --gpu-index <device_index>        Use a specific GPU (run with --verbose to get available device list).\n");
	OS::get_singleton()->print("  --text-driver <driver>            Text driver (Fonts, BiDi, shaping).\n");
	OS::get_singleton()->print("  --tablet-driver <driver>          Pen tablet input driver.\n");
	OS::get_singleton()->print("  --headless                        Enable headless mode (--display-driver headless --audio-driver Dummy). Useful for servers and with --script.\n");
	OS::get_singleton()->print("  --write-movie <file>              Writes a video to the specified path (usually with .avi or .png extension).\n");
	OS::get_singleton()->print("                                    --fixed-fps is forced when enabled, but it can be used to change movie FPS.\n");
	OS::get_singleton()->print("                                    --disable-vsync can speed up movie writing but makes interaction more difficult.\n");
	OS::get_singleton()->print("\n");
	OS::get_singleton()->print("Display options:\n");
	OS::get_singleton()->print("  -f, --fullscreen                  Request fullscreen mode.\n");
	OS::get_singleton()->print("  -m, --maximized                   Request a maximized window.\n");
	OS::get_singleton()->print("  -w, --windowed                    Request windowed mode.\n");
	OS::get_singleton()->print("  -t, --always-on-top               Request an always-on-top window.\n");
	OS::get_singleton()->print("  --resolution <W>x<H>              Request window resolution.\n");
	OS::get_singleton()->print("  --position <X>,<Y>                Request window position (if set, screen argument is ignored).\n");
	OS::get_singleton()->print("  --screen <N>                      Request window screen.\n");
	OS::get_singleton()->print("  --single-window                   Use a single window (no separate subwindows).\n");
	OS::get_singleton()->print("  --xr-mode <mode>                  Select XR (Extended Reality) mode ['default', 'off', 'on'].\n");
	OS::get_singleton()->print("\n");
	OS::get_singleton()->print("Debug options:\n");
	OS::get_singleton()->print("  -d, --debug                       Debug (local stdout debugger).\n");
	OS::get_singleton()->print("  -b, --breakpoints                 Breakpoint list as source::line comma-separated pairs, no spaces (use %%20 instead).\n");
	OS::get_singleton()->print("  --profiling                       Enable profiling in the script debugger.\n");
	OS::get_singleton()->print("  --gpu-profile                     Show a GPU profile of the tasks that took the most time during frame rendering.\n");
	OS::get_singleton()->print("  --gpu-validation                  Enable graphics API validation layers for debugging.\n");
#if DEBUG_ENABLED
	OS::get_singleton()->print("  --gpu-abort                       Abort on graphics API usage errors (usually validation layer errors). May help see the problem if your system freezes.\n");