[tuple.helper] Remove redundant 'public' in base-specifier of struct (#7539)

Author: AlisdairM

source/utilities.tex

@@ -2751,7 +2751,7 @@
 \indexlibraryglobal{tuple_size}%
 \begin{itemdecl}
 template<class... Types>
-  struct tuple_size<tuple<Types...>> : public integral_constant<size_t, sizeof...(Types)> { };
+  struct tuple_size<tuple<Types...>> : integral_constant<size_t, sizeof...(Types)> { };
 \end{itemdecl}
 
 \indexlibraryglobal{tuple_element}%