### 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
use_startup_benchmark = false;
			startup_benchmark_file = String();
		}
#endif
		GLOBAL_DEF_BASIC(PropertyInfo(Variant::STRING, "display/window/stretch/mode", PROPERTY_HINT_ENUM, "disabled,canvas_items,viewport"), "disabled");
		GLOBAL_DEF_BASIC(PropertyInfo(Variant::STRING, "display/window/stretch/aspect", PROPERTY_HINT_ENUM, "ignore,keep,keep_width,keep_height,expand"), "keep");
		GLOBAL_DEF_BASIC(PropertyInfo(Variant::FLOAT, "display/window/stretch/scale", PROPERTY_HINT_RANGE, "0.5,8.0,0.01"), 1.0);
		sml->set_auto_accept_quit(GLOBAL_DEF("application/config/auto_accept_quit", true));
		sml->set_quit_on_go_back(GLOBAL_DEF("application/config/quit_on_go_back", true));
		GLOBAL_DEF_BASIC("gui/common/snap_controls_to_pixels", true);
		GLOBAL_DEF_BASIC("gui/fonts/dynamic_fonts/use_oversampling", true);
		GLOBAL_DEF_BASIC(PropertyInfo(Variant::INT, "rendering/textures/canvas_textures/default_texture_filter", PROPERTY_HINT_ENUM, "Nearest,Linear,Linear Mipmap,Nearest Mipmap"), 1);
		GLOBAL_DEF_BASIC(PropertyInfo(Variant::INT, "rendering/textures/canvas_textures/default_texture_repeat", PROPERTY_HINT_ENUM, "Disable,Enable,Mirror"), 0);
		if (!editor && !project_manager) {
			/
			String stretch_mode = GLOBAL_GET("display/window/stretch/mode");
			String stretch_aspect = GLOBAL_GET("display/window/stretch/aspect");
			Size2i stretch_size = Size2i(GLOBAL_GET("display/window/size/viewport_width"),
					GLOBAL_GET("display/window/size/viewport_height"));
			real_t stretch_scale = GLOBAL_GET("display/window/stretch/scale");
			Window::ContentScaleMode cs_sm = Window::CONTENT_SCALE_MODE_DISABLED;
			if (stretch_mode == "canvas_items") {
				cs_sm = Window::CONTENT_SCALE_MODE_CANVAS_ITEMS;
			} else if (stretch_mode == "viewport") {
				cs_sm = Window::CONTENT_SCALE_MODE_VIEWPORT;
			}
			Window::ContentScaleAspect cs_aspect = Window::CONTENT_SCALE_ASPECT_IGNORE;
			if (stretch_aspect == "keep") {
				cs_aspect = Window::CONTENT_SCALE_ASPECT_KEEP;
			} else if (stretch_aspect == "keep_width") {