Remove unused constructors from backing container

Removing this constructor simplifies the interface, by reducing the
number of different ways to construct the classes and avoiding exposing
the implementation detail of what type of container `json_objectt` and
`json_arrayt` are backed by.

Author: thomasspriggs

src/util/json.h

@@ -161,11 +161,6 @@ class json_arrayt:public jsont
   {
   }
 
-  explicit json_arrayt(arrayt &&entries)
-    : jsont(kindt::J_ARRAY, std::move(entries))
-  {
-  }
-
   explicit json_arrayt(std::initializer_list<jsont> &&initializer_list)
     : jsont(kindt::J_ARRAY, arrayt{initializer_list})
   {
@@ -305,11 +300,6 @@ class json_objectt:public jsont
   {
   }
 
-  explicit json_objectt(objectt &&objects)
-    : jsont(kindt::J_OBJECT, std::move(objects))
-  {
-  }
-
   explicit json_objectt(
     std::initializer_list<typename objectt::value_type> &&initializer_list)
     : jsont(kindt::J_OBJECT, objectt{initializer_list})