eo: do not expose callback,add and del events in bindings

These events have been removed from efl_object.eo. Bindings can
still use the EFL_EVENT_CALLBACK_ADD and EFL_EVENT_CALLBACK_DEL
events from C, but they won't be available to the bound language.
The rationale is that bound languages probably will have their
own way to handle callbacks and C function pointers will mean
very little to them. For example, the binding code could route
the native callback through a dispatcher so the received
function ptr would always be that of the dispatcher method.

Closes D6179.

src/lib/eo/Eo.h

@@ -2116,6 +2116,18 @@ eina_value_object_get(Eina_Value *v)
    return r;
 }
 
+/**
+ * @brief Event triggered when a callback was added to the object
+ */
+#define EFL_EVENT_CALLBACK_ADD (&(_EFL_EVENT_CALLBACK_ADD))
+EAPI extern const Efl_Event_Description _EFL_EVENT_CALLBACK_ADD;
+
+/**
+ * @brief Event triggered when a callback was removed from the object
+ */
+#define EFL_EVENT_CALLBACK_DEL (&(_EFL_EVENT_CALLBACK_DEL))
+EAPI extern const Efl_Event_Description _EFL_EVENT_CALLBACK_DEL;
+
 /**
  * @}
  */

src/lib/eo/efl_object.eo

@@ -303,8 +303,6 @@ abstract Efl.Object ()
         class.destructor;
    }
    events {
-      callback,add @hot; [[A callback was added.]]
-      callback,del @hot; [[A callback was deleted.]]
       del @hot; [[Object is being deleted.]]
       invalidate @hot; [[Object is being invalidated and loosing its parent.]]
       noref @hot; [[Object has lost its last reference, only parent relationship is keeping it alive.]]

src/lib/eo/eo_base_class.c

@@ -12,6 +12,12 @@
 
 #define EFL_EVENT_SPECIAL_SKIP 1
 
+EAPI const Efl_Event_Description _EFL_EVENT_CALLBACK_ADD =
+    EFL_EVENT_DESCRIPTION_HOT("callback,add");
+
+EAPI const Efl_Event_Description _EFL_EVENT_CALLBACK_DEL =
+    EFL_EVENT_DESCRIPTION_HOT("callback,del");
+
 static int event_freeze_count = 0;
 
 typedef struct _Eo_Callback_Description  Eo_Callback_Description;