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/widget/button/icon.rs

@@ -156,7 +156,7 @@ impl<'a, Message: Clone + 'static> From<Button<'a, Message>> for Element<'a, Mes
             );
         }
 
-        let mut button = if builder.variant.vertical {
+        let button = if builder.variant.vertical {
             crate::widget::column::with_children(content)
                 .padding(builder.padding)
                 .spacing(builder.spacing)
@@ -173,9 +173,11 @@ impl<'a, Message: Clone + 'static> From<Button<'a, Message>> for Element<'a, Mes
         };
 
         #[cfg(feature = "a11y")]
-        {
+        let button = {
+            let mut button = button;
             button = button.name(builder.name).description(builder.description);
-        }
+            button
+        };
 
         let button = button
             .padding(0)