Remove the old didFirstVisuallyNonEmptyLayout hook.

Source/core/loader/EmptyClients.h

Index: Source/core/loader/EmptyClients.h
diff --git a/Source/core/loader/EmptyClients.h b/Source/core/loader/EmptyClients.h
index a9487af1022820840bfd5cee4d3716c2f8359ab1..463f2b6873c259503affa4c701e41e6e926493ee 100644
--- a/Source/core/loader/EmptyClients.h
+++ b/Source/core/loader/EmptyClients.h
@@ -202,7 +202,6 @@ public:
     void dispatchDidFailLoad(const ResourceError&, HistoryCommitType) override {}
     void dispatchDidFinishDocumentLoad(bool) override {}
     void dispatchDidFinishLoad() override {}
-    void dispatchDidFirstVisuallyNonEmptyLayout() override {}
     void dispatchDidChangeThemeColor() override {}
 
     NavigationPolicy decidePolicyForNavigation(const ResourceRequest&, DocumentLoader*, NavigationPolicy) override;