Override Elm_Interface_Atspi_Accessible.relationships_clear

Override Elm_Interface_Atspi_Accessible.relationships_clear

   The elm_widget, elm_widget_item override following interfaces.

     - Elm_Interface_Atspi_Accessible.relationship_append
     - Elm_Interface_Atspi_Accessible.relationship_remove

   And keeps the relationship information in its data structure.
   So the elm_atspi_accessible_relationships_clear does not work.

   +)
   atspi: add new APIs for setting atspi relationship.
      Introduce new APIs elm_object_atspi_relationship_append and
      elm_object_atspi_relationship_remove allowing to set developer-defined
      accessibility relationships between widgets.
      @tizen_feature
         commit : 6992c77377e7b85e183b7f56be574b0aff206076

Change-Id: I11290fc219719c9589418cc79ad8b8884220f7d4