Using ordered_json instead of fifo_map in test-regression

This is more comprehensive and the "my_workaround_fifo_map" wrapper does not allow to infer value type as required in this branch.

This reverts commit 064a9c9.

Author: gatopeich

include/nlohmann/json.hpp

@@ -496,9 +496,7 @@ class basic_json
     using object_t = ObjectType<StringType,
           basic_json,
           object_comparator_t,
-          // Note: instantiating ObjectType with dummy allocator to extract ::value_type
-          AllocatorType<typename ObjectType<StringType, basic_json, object_comparator_t, AllocatorType<int>
-                                            >::value_type>>;
+          AllocatorType<typename ObjectType<StringType, basic_json>::value_type>>;
 
     /*!
     @brief a type for an array

single_include/nlohmann/json.hpp

@@ -16348,9 +16348,7 @@ class basic_json
     using object_t = ObjectType<StringType,
           basic_json,
           object_comparator_t,
-          // Note: instantiating ObjectType with dummy allocator to extract ::value_type
-          AllocatorType<typename ObjectType<StringType, basic_json, object_comparator_t, AllocatorType<int>
-                                            >::value_type>>;
+          AllocatorType<typename ObjectType<StringType, basic_json>::value_type>>;
 
     /*!
     @brief a type for an array

test/src/unit-regression.cpp

@@ -52,15 +52,11 @@ using nlohmann::json;
     #include <variant>
 #endif
 
-#include "fifo_map.hpp"
-
 /////////////////////////////////////////////////////////////////////
 // for #972
 /////////////////////////////////////////////////////////////////////
 
-template<class K, class V, class dummy_compare, class A>
-using my_workaround_fifo_map = nlohmann::fifo_map<K, V, nlohmann::fifo_map_compare<K>, A>;
-using my_json = nlohmann::basic_json<my_workaround_fifo_map>;
+using my_json = nlohmann::ordered_json;
 
 /////////////////////////////////////////////////////////////////////
 // for #977