Clean up LayoutShadowRootHelpers::get_style_data_for_layout

Parameter E is unused and the result should be bound by 'dom.

components/layout_thread_2020/dom_wrapper.rs

@@ -184,12 +184,7 @@ impl<'lr> TShadowRoot for ServoShadowRoot<'lr> {
     where
         Self: 'a,
     {
-        Some(unsafe {
-            &self
-                .shadow_root
-                .get_style_data_for_layout::<ServoLayoutElement>()
-                .data
-        })
+        Some(unsafe { &self.shadow_root.get_style_data_for_layout().data })
     }
 }