[PATCH] Remove unused std::_Iter_base class template

[Jonathan Wakely]

This class template has been unused since __gnu_debug::__base was
removed in r263786.

        * include/bits/stl_iterator_base_types.h (_Iter_base): Remove unused
        class template and partial specialization.

Tested x86_64-linux (normal and debug mode), committed to trunk.


commit f87489c246a3a1c2399ab00e1c1c099f66257779
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Mon Apr 29 11:58:15 2019 +0100

    Remove unused std::_Iter_base class template
    
    This class template has been unused since __gnu_debug::__base was
    removed in r263786.
    
            * include/bits/stl_iterator_base_types.h (_Iter_base): Remove unused
            class template and partial specialization.

diff --git a/libstdc++-v3/include/bits/stl_iterator_base_types.h 
b/libstdc++-v3/include/bits/stl_iterator_base_types.h
index 4920b61a840..af69dbb017a 100644
--- a/libstdc++-v3/include/bits/stl_iterator_base_types.h
+++ b/libstdc++-v3/include/bits/stl_iterator_base_types.h
@@ -207,26 +207,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   //@}
 
-#if __cplusplus < 201103L
-  // If _Iterator has a base returns it otherwise _Iterator is returned
-  // untouched
-  template<typename _Iterator, bool _HasBase>
-    struct _Iter_base
-    {
-      typedef _Iterator iterator_type;
-      static iterator_type _S_base(_Iterator __it)
-      { return __it; }
-    };
-
-  template<typename _Iterator>
-    struct _Iter_base<_Iterator, true>
-    {
-      typedef typename _Iterator::iterator_type iterator_type;
-      static iterator_type _S_base(_Iterator __it)
-      { return __it.base(); }
-    };
-#endif
-
 #if __cplusplus >= 201103L
   template<typename _InIter>
     using _RequireInputIter = typename