LibWeb: Remove unused `TableCellBox::next_cell()`

Userland/Libraries/LibWeb/Layout/TableCellBox.h

@@ -18,9 +18,6 @@ public:
     TableCellBox(DOM::Document&, DOM::Element*, CSS::ComputedValues);
     virtual ~TableCellBox() override;
 
-    TableCellBox* next_cell() { return next_sibling_of_type<TableCellBox>(); }
-    TableCellBox const* next_cell() const { return next_sibling_of_type<TableCellBox>(); }
-
     size_t colspan() const;
     size_t rowspan() const;