[NFC][libc++][span] Implement LWG3903 (span destructor is redundantly noexcept)

[yronglin]

Summary

Implement LWG3903 (span destructor is redundantly noexcept) https://wg21.link/LWG3903

This patch just remove the commented destructor.

[yronglin]

duplicated

libcxx/docs/Status/Cxx2cIssues.csv

 "Issue #","Issue Name","Meeting","Status","First released version","Labels"
 "`2994 <https://wg21.link/LWG2994>`__","Needless UB for ``basic_string`` and ``basic_string_view``","Varna June 2023","","",""
 "`3884 <https://wg21.link/LWG3884>`__","``flat_foo`` is missing allocator-extended copy/move constructors","Varna June 2023","","","|flat_containers|"
 "`3885 <https://wg21.link/LWG3885>`__","``op`` should be in [zombie.names]","Varna June 2023","","",""
 "`3887 <https://wg21.link/LWG3887>`__","Version macro for ``allocate_at_least``","Varna June 2023","","",""
 "`3893 <https://wg21.link/LWG3893>`__","LWG 3661 broke ``atomic<shared_ptr<T>> a; a = nullptr;``","Varna June 2023","","",""
 "`3894 <https://wg21.link/LWG3894>`__","``generator::promise_type::yield_value(ranges::elements_of<Rng, Alloc>)`` should not be ``noexcept``","Varna June 2023","","",""
-"`3903 <https://wg21.link/LWG3903>`__","span destructor is redundantly noexcept","Varna June 2023","","",""
+"`3903 <https://wg21.link/LWG3903>`__","span destructor is redundantly noexcept","Varna June 2023","|Complete|","17.0",""
 "`3904 <https://wg21.link/LWG3904>`__","``lazy_split_view::outer-iterator``'s const-converting constructor isn't setting ``trailing_empty_``","Varna June 2023","","","|ranges|"
 "`3905 <https://wg21.link/LWG3905>`__","Type of ``std::fexcept_t``","Varna June 2023","","",""
 "`3912 <https://wg21.link/LWG3912>`__","``enumerate_view::iterator::operator-`` should be ``noexcept``","Varna June 2023","","","|ranges|"
 "`3914 <https://wg21.link/LWG3914>`__","Inconsistent template-head of ``ranges::enumerate_view``","Varna June 2023","","","|ranges|"
 "`3915 <https://wg21.link/LWG3915>`__","Redundant paragraph about expression variations","Varna June 2023","","","|ranges|"
 "`3925 <https://wg21.link/LWG3925>`__","Concept ``formattable``'s definition is incorrect","Varna June 2023","|Complete|","17.0","|format|"
 "`3927 <https://wg21.link/LWG3927>`__","Unclear preconditions for ``operator[]`` for sequence containers","Varna June 2023","|Nothing To Do|","",""
 "`3935 <https://wg21.link/LWG3935>`__","``template<class X> constexpr complex& operator=(const complex<X>&)`` has no specification","Varna June 2023","|Complete|","Clang 3.4",""
 "`3938 <https://wg21.link/LWG3938>`__","Cannot use ``std::expected`` monadic ops with move-only ``error_type``","Varna June 2023","","",""
 "`3940 <https://wg21.link/LWG3940>`__","``std::expected<void, E>::value()`` also needs ``E`` to be copy constructible","Varna June 2023","","",""
 "","","","","",""
 "`3343 <https://wg21.link/LWG3343>`__","Ordering of calls to ``unlock()`` and ``notify_all()`` in Effects element of ``notify_all_at_thread_exit()`` should be reversed","Not Yet Adopted","|Complete|","16.0",""
 "`3892 <https://wg21.link/LWG3892>`__","Incorrect formatting of nested ranges and tuples","Not Yet Adopted","|Complete|","17.0","|format|"
 "","","","","",""

libcxx/include/span

template <size_t N>
         constexpr span(array<value_type, N>& arr) noexcept;
     template <size_t N>
         constexpr span(const array<value_type, N>& arr) noexcept;
     template<class R>
       constexpr explicit(Extent != dynamic_extent) span(R&& r);
     constexpr span(const span& other) noexcept = default;
     template <class OtherElementType, size_t OtherExtent>
         constexpr explicit(Extent != dynamic_extent) span(const span<OtherElementType, OtherExtent>& s) noexcept;
-    ~span() noexcept = default;
     constexpr span& operator=(const span& other) noexcept = default;
 
     // [span.sub], span subviews
     template <size_t Count>
         constexpr span<element_type, Count> first() const;
     template <size_t Count>
         constexpr span<element_type, Count> last() const;
     template <size_t Offset, size_t Count = dynamic_extent>
// [span.cons], span constructors, copy, assignment, and destructor
 
     template <__span_array_convertible<element_type> _OtherElementType>
     _LIBCPP_INLINE_VISIBILITY
         constexpr explicit span(const span<_OtherElementType, dynamic_extent>& __other) noexcept
         : __data_{__other.data()} {
           _LIBCPP_ASSERT_UNCATEGORIZED(_Extent == __other.size(), "size mismatch in span's constructor (other span)");
         }
 
-
-//  ~span() noexcept = default;
-
     template <size_t _Count>
     _LIBCPP_INLINE_VISIBILITY
     constexpr span<element_type, _Count> first() const noexcept
     {
         static_assert(_Count <= _Extent, "span<T, N>::first<Count>(): Count out of range");
         return span<element_type, _Count>{data(), _Count};
     }
 
// [span.cons], span constructors, copy, assignment, and destructor
     _LIBCPP_INLINE_VISIBILITY
     constexpr span(_Range&& __r) : __data_(ranges::data(__r)), __size_{ranges::size(__r)} {}
 
     template <__span_array_convertible<element_type> _OtherElementType, size_t _OtherExtent>
     _LIBCPP_INLINE_VISIBILITY
         constexpr span(const span<_OtherElementType, _OtherExtent>& __other)  noexcept
         : __data_{__other.data()}, __size_{__other.size()} {}
 
-//    ~span() noexcept = default;
-
     template <size_t _Count>
     _LIBCPP_INLINE_VISIBILITY
     constexpr span<element_type, _Count> first() const noexcept
     {
         _LIBCPP_ASSERT_UNCATEGORIZED(_Count <= size(), "span<T>::first<Count>(): Count out of range");
         return span<element_type, _Count>{data(), _Count};
     }