[libc++][NFC] Remove unused functions from <__split_buffer> (#115735)

Author: philnik777

libcxx/include/__split_buffer

@@ -139,7 +139,6 @@ public:
   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI reference back() { return *(__end_ - 1); }
   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI const_reference back() const { return *(__end_ - 1); }
 
-  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void reserve(size_type __n);
   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void shrink_to_fit() _NOEXCEPT;
 
   template <class... _Args>
@@ -153,9 +152,6 @@ public:
   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __construct_at_end(size_type __n);
   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __construct_at_end(size_type __n, const_reference __x);
 
-  template <class _InputIter, __enable_if_t<__has_exactly_input_iterator_category<_InputIter>::value, int> = 0>
-  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __construct_at_end(_InputIter __first, _InputIter __last);
-
   template <class _ForwardIterator, __enable_if_t<__has_forward_iterator_category<_ForwardIterator>::value, int> = 0>
   _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void
   __construct_at_end(_ForwardIterator __first, _ForwardIterator __last);
@@ -260,13 +256,6 @@ __split_buffer<_Tp, _Allocator>::__construct_at_end(size_type __n, const_referen
   }
 }
 
-template <class _Tp, class _Allocator>
-template <class _InputIter, __enable_if_t<__has_exactly_input_iterator_category<_InputIter>::value, int> >
-_LIBCPP_CONSTEXPR_SINCE_CXX20 void
-__split_buffer<_Tp, _Allocator>::__construct_at_end(_InputIter __first, _InputIter __last) {
-  __construct_at_end_with_sentinel(__first, __last);
-}
-
 template <class _Tp, class _Allocator>
 template <class _Iterator, class _Sentinel>
 _LIBCPP_CONSTEXPR_SINCE_CXX20 void
@@ -414,18 +403,6 @@ _LIBCPP_CONSTEXPR_SINCE_CXX20 void __split_buffer<_Tp, _Allocator>::swap(__split
   std::__swap_allocator(__alloc_, __x.__alloc_);
 }
 
-template <class _Tp, class _Allocator>
-_LIBCPP_CONSTEXPR_SINCE_CXX20 void __split_buffer<_Tp, _Allocator>::reserve(size_type __n) {
-  if (__n < capacity()) {
-    __split_buffer<value_type, __alloc_rr&> __t(__n, 0, __alloc_);
-    __t.__construct_at_end(move_iterator<pointer>(__begin_), move_iterator<pointer>(__end_));
-    std::swap(__first_, __t.__first_);
-    std::swap(__begin_, __t.__begin_);
-    std::swap(__end_, __t.__end_);
-    std::swap(__end_cap_, __t.__end_cap_);
-  }
-}
-
 template <class _Tp, class _Allocator>
 _LIBCPP_CONSTEXPR_SINCE_CXX20 void __split_buffer<_Tp, _Allocator>::shrink_to_fit() _NOEXCEPT {
   if (capacity() > size()) {