remove deprecated init-list behavior

include/boost/json/impl/value.ipp

@@ -238,15 +238,13 @@ value(
     }
     else
     {
-#ifndef BOOST_JSON_LEGACY_INIT_LIST_BEHAVIOR
         if( init.size() == 1 )
         {
             ::new(&sca_) scalar();
             value temp = init.begin()->make_value( std::move(sp) );
             swap(temp);
         }
         else
-#endif
         {
             ::new(&arr_) array(
                 value_ref::make_array(

include/boost/json/value.hpp

@@ -1029,20 +1029,6 @@ class value
         @param sp A pointer to the `boost::container::pmr::memory_resource` to
         use. The container will acquire shared ownership of the memory
         resource.
-
-        @par Note
-        The previous behavior of this constructor was to always
-        construct either an @ref object or an @ref array. In practice though,
-        several C++ implementations did not treat `value{x}` as a constructor
-        from initializer list. This effectively resulted in different behavior
-        on different implementations. <br>
-
-        If you need the legacy behavior define macro
-        `BOOST_JSON_LEGACY_INIT_LIST_BEHAVIOR` when you are building the
-        library. The macro and the functionality will be deprecated in the
-        future and then removed, so we urge you to change your code for the new
-        behavior as soon as possible. The simplest way to create an @ref array
-        with 1 element using an initializer list is via `array{x}`.
     */
     BOOST_JSON_DECL
     value(

test/value.cpp

@@ -2398,7 +2398,6 @@ class value_test
             BOOST_TEST(( jv6 == array{1,2} ));
         }
         {
-#ifndef BOOST_JSON_LEGACY_INIT_LIST_BEHAVIOR
             value jv1{0};
             BOOST_TEST( jv1 == 0 );
 
@@ -2408,7 +2407,6 @@ class value_test
             value jv3 = value{0};
             BOOST_TEST( jv3 == 0 );
 
-#endif
             value jv4{{0}};
             BOOST_TEST( jv4 == array{0} );