Really fix the off-by-one error in json_array_remove()

It didn't affect only the last element but all of them. One item too
much was always moved.

src/value.c

@@ -511,7 +511,7 @@ int json_array_remove(json_t *json, size_t index)
 
     /* If we're removing the last element, nothing has to be moved */
     if(index < array->entries - 1)
-        array_move(array, index, index + 1, array->entries - index);
+        array_move(array, index, index + 1, array->entries - index - 1);
 
     array->entries--;