Remove several unused forward declarations. Fixes PR22605.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@229728 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/iterator b/include/iterator
index 05d7412..04ff4c1 100644
--- a/include/iterator
+++ b/include/iterator
@@ -1112,8 +1112,6 @@
 >::type
 __unwrap_iter(__wrap_iter<_Tp*>);
 
-template <class _Tp, class _Alloc> class _LIBCPP_TYPE_VIS_ONLY vector;
-
 template <class _Iter>
 class __wrap_iter
 {
@@ -1243,7 +1241,7 @@
 
     template <class _Up> friend class __wrap_iter;
     template <class _CharT, class _Traits, class _Alloc> friend class basic_string;
-    template <class _Tp, class _Alloc> friend class vector;
+    template <class _Tp, class _Alloc> friend class _LIBCPP_TYPE_VIS_ONLY vector;
 
     template <class _Iter1, class _Iter2>
     friend