LibGUI: Remove Model::row_name() since nothing used it

Libraries/LibGUI/Model.h

@@ -67,7 +67,6 @@ public:
 
     virtual int row_count(const ModelIndex& = ModelIndex()) const = 0;
     virtual int column_count(const ModelIndex& = ModelIndex()) const = 0;
-    virtual String row_name(int) const { return {}; }
     virtual String column_name(int) const { return {}; }
     virtual Variant data(const ModelIndex&, Role = Role::Display) const = 0;
     virtual void update() = 0;

Libraries/LibGUI/SortingProxyModel.cpp

@@ -64,11 +64,6 @@ ModelIndex SortingProxyModel::map_to_target(const ModelIndex& index) const
     return target().index(m_row_mappings[index.row()], index.column());
 }
 
-String SortingProxyModel::row_name(int index) const
-{
-    return target().row_name(index);
-}
-
 String SortingProxyModel::column_name(int index) const
 {
     return target().column_name(index);

Libraries/LibGUI/SortingProxyModel.h

@@ -37,7 +37,6 @@ public:
 
     virtual int row_count(const ModelIndex& = ModelIndex()) const override;
     virtual int column_count(const ModelIndex& = ModelIndex()) const override;
-    virtual String row_name(int) const override;
     virtual String column_name(int) const override;
     virtual Variant data(const ModelIndex&, Role = Role::Display) const override;
     virtual void update() override;