Remove warm-up of demo app

Since https://github.com/emilk/egui/pull/1149 we only update the
region of the font atlas that has changes, so loading new glyphs is much
cheaper. This means warm-up is much less needed.

There is now a small delay when opening the font book,
but not when opening anything else.

egui_demo_lib/src/wrap_app.rs

@@ -67,11 +67,6 @@ impl epi::App for WrapApp {
         egui::Rgba::TRANSPARENT // we set a `CentralPanel` fill color in `demo_windows.rs`
     }
 
-    fn warm_up_enabled(&self) -> bool {
-        // The example windows use a lot of emojis. Pre-cache them by running one frame where everything is open
-        cfg!(not(debug_assertions))
-    }
-
     fn update(&mut self, ctx: &egui::Context, frame: &epi::Frame) {
         if let Some(web_info) = frame.info().web_info.as_ref() {
             if let Some(anchor) = web_info.web_location_hash.strip_prefix('#') {