[iterator.synopsis] Apply changes of P2538R1 to the synopsis of <iterator> (#7841)

Remove `incrementable_traits<projected>` and update `projected`.

Author: frederick-vs-ja

source/iterators.tex

@@ -169,10 +169,7 @@
 
   // \ref{projected}, projected
   template<@\libconcept{indirectly_readable}@ I, @\libconcept{indirectly_regular_unary_invocable}@<I> Proj>
-    struct projected;                                                               // freestanding
-
-  template<@\libconcept{weakly_incrementable}@ I, class Proj>
-    struct incrementable_traits<projected<I, Proj>>;                                // freestanding
+    using projected = @\seebelow@;                                                    // freestanding
 
   template<@\libconcept{indirectly_readable}@ I, @\libconcept{indirectly_regular_unary_invocable}@<I> Proj>
   using projected_value_t =                                                         // freestanding