While applying N4258, I forgot about LWG#2455, which modified the modifications. Correct those - h/t: Howard

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@239004 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/string b/include/string
index b8cbea3..ac7b30a 100644
--- a/include/string
+++ b/include/string
@@ -1321,11 +1321,7 @@
     static const size_type npos = -1;
 
     _LIBCPP_INLINE_VISIBILITY basic_string()
-#if _LIBCPP_STD_VER <= 14
         _NOEXCEPT_(is_nothrow_default_constructible<allocator_type>::value);
-#else
-        _NOEXCEPT;
-#endif
 
     _LIBCPP_INLINE_VISIBILITY explicit basic_string(const allocator_type& __a)
 #if _LIBCPP_STD_VER <= 14
@@ -1943,11 +1939,7 @@
 template <class _CharT, class _Traits, class _Allocator>
 inline _LIBCPP_INLINE_VISIBILITY
 basic_string<_CharT, _Traits, _Allocator>::basic_string()
-#if _LIBCPP_STD_VER <= 14
-        _NOEXCEPT_(is_nothrow_default_constructible<allocator_type>::value)
-#else
-        _NOEXCEPT
-#endif
+    _NOEXCEPT_(is_nothrow_default_constructible<allocator_type>::value)
 {
 #if _LIBCPP_DEBUG_LEVEL >= 2
     __get_db()->__insert_c(this);