remove stuff from arena_allocator and use ref_type_t in bad expr test

Author: SteveBronder

stan/math/rev/core/arena_allocator.hpp

@@ -13,13 +13,6 @@ namespace math {
 template <typename T>
 struct arena_allocator {
   using value_type = T;
-  using pointer = T*;
-  using const_pointer = const T*;
-  using reference = T&;
-  using const_reference = const T&;
-  using size_type = size_t;
-  using difference_type = ptrdiff_t;
-  using propagate_on_container_move_assignment = std::true_type;
 
   /**
    * Allocates space for `n` items of type `T`.
@@ -30,13 +23,6 @@ struct arena_allocator {
   T* allocate(std::size_t n) {
     return ChainableStack::instance_->memalloc_.alloc_array<T>(n);
   }
-  /**
-   * Returns the maximum theoretically possible value of n,
-   *  for which the call allocate(n, 0) could succeed.
-   */
-  static constexpr size_type max_size() noexcept {
-    return std::numeric_limits<size_type>::max() / sizeof(T);
-  }
 
   /**
    * No-op. Memory is deallocated by calling `recover_memory()`.

test/expressions/expression_test_helpers.hpp

@@ -282,7 +282,7 @@ auto bad_wrong_value(const T& a) {
 
 template <typename T>
 auto bad_wrong_derivatives(const T& a) {
-  operands_and_partials<plain_type_t<T>> ops(a);
+  operands_and_partials<ref_type_t<T>> ops(a);
   if (!is_constant<T>::value && std::is_same<T, plain_type_t<T>>::value) {
     ops.edge1_.partials_[0] = 1234;
   }