alloc/chunked: remove local fwd decl for std::pmr::memory_resource

alloc/chunked.hpp

@@ -8,48 +8,12 @@
 
 #pragma once
 
-#if 0 && __has_include(<memory_resource>)
+#include <memory_resource>
-    #include <memory_resource>
-#else
-    #include <cstddef>
-#endif
 
 #include <memory>
 #include <vector>
 
 
-namespace std::pmr {
-    class memory_resource {
-    public:
-        memory_resource () = default;
-        memory_resource (memory_resource const&) = default;
-        memory_resource& operator= (memory_resource const&) = default;
-        virtual ~memory_resource () = default;
-
-        [[nodiscard]] void* allocate (
-            std::size_t bytes,
-            std::size_t alignment = alignof (std::max_align_t)
-        ) { return do_allocate (bytes, alignment); }
-
-        void deallocate(
-            void* p,
-            std::size_t bytes,
-            std::size_t alignment = alignof(std::max_align_t)
-        ) { return do_deallocate (p, bytes, alignment); }
-
-        bool is_equal (memory_resource const &rhs) const noexcept
-        {
-            return do_is_equal (rhs);
-        }
-
-    private:
-        virtual void *do_allocate (std::size_t bytes, std::size_t alignment) = 0;
-        virtual void do_deallocate (void *p, std::size_t bytes, std::size_t alignment) = 0;
-        virtual bool do_is_equal (memory_resource const&) const noexcept = 0;
-    };
-}
-
-
 ///////////////////////////////////////////////////////////////////////////////
 namespace cruft::alloc {
     /// An unbounded contiguous allocator that operates on chunks, similar to