yoda: warning cleanup sweep (dead code + clippy --fix) (squashed)

Squash of 4 yoda commits:
- 84437e21 yoda: libcosmic-yoda dead-code purge (14->0 warnings)
- 999db0a4 yoda: cosmic-theme cleanup (4->0 warnings) — workspace at 0 warnings total
- 4743bb8e yoda: cargo clippy --fix on libcosmic-yoda (115->33 warnings)
- 675f3b59 chore: reduce local stack warnings

src/app/mod.rs

@@ -284,7 +284,7 @@ where
                 // app = app.window(window_settings);
                 core.main_window = Some(iced_core::window::Id::RESERVED);
             }
-            let mut app = iced::daemon(
+            let app = iced::daemon(
                 BootData(Rc::new(RefCell::new(Some(BootDataInner::<App> {
                     flags,
                     core,