use std::destroy_at in folly::dynamic

Summary: Replace use of `folly::detail::Destroy::destroy` with `std::destroy_at`, available since C++17, in `folly::dynamic`.

Reviewed By: ilvokhin

Differential Revision: D77837325

fbshipit-source-id: db8d0f5fcc99ceacac422588880a2c8c40142e4e

Author: yfeldblum

third-party/folly/src/folly/json/dynamic-inl.h

@@ -130,15 +130,6 @@ struct FOLLY_EXPORT TypeError : std::runtime_error {
 
 namespace detail {
 
-// This helper is used in destroy() to be able to run destructors on
-// types like "int64_t" without a compiler error.
-struct Destroy {
-  template <class T>
-  static void destroy(T* t) {
-    t->~T();
-  }
-};
-
 /*
  * Helper for implementing numeric conversions in operators on
  * numbers.  Just promotes to double when one of the arguments is

third-party/folly/src/folly/json/dynamic.cpp

@@ -386,7 +386,7 @@ void dynamic::destroy() noexcept {
     return;
   }
 
-#define FB_X(T) detail::Destroy::destroy(getAddress<T>())
+#define FB_X(T) std::destroy_at(getAddress<T>())
   FB_DYNAMIC_APPLY(type_, FB_X);
 #undef FB_X
 }