[iterator.synopsis] Remove blank extra line (#7619)

Author: Andreas-Krug

source/iterators.tex

@@ -174,7 +174,6 @@
   template<@\libconcept{weakly_incrementable}@ I, class Proj>
     struct incrementable_traits<projected<I, Proj>>;                                // freestanding
 
-
   template<@\libconcept{indirectly_readable}@ I, @\libconcept{indirectly_regular_unary_invocable}@<I> Proj>
   using projected_value_t =                                                         // freestanding
     remove_cvref_t<invoke_result_t<Proj&, iter_value_t<I>&>>;