efl_pack: move layout,updated event to Efl.Pack_Layout

Summary:
'layout,updated' event is more suitable for Efl.Pack_Layout which have
layout_update method.

Test Plan: make

Reviewers: segfaultxavi, cedric, Jaehyun_Cho

Reviewed By: segfaultxavi, Jaehyun_Cho

Subscribers: #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D7906

src/lib/efl/interfaces/efl_pack.eo

@@ -57,7 +57,4 @@ interface Efl.Pack extends Efl.Container
          }
       }
    }
-   events {
-      layout,updated: void; [[Sent after the layout was updated.]]
-   }
 }

src/lib/efl/interfaces/efl_pack_layout.eo

@@ -23,4 +23,7 @@ interface Efl.Pack_Layout
          ]]
       }
    }
+   events {
+      layout,updated: void; [[Sent after the layout was updated.]]
+   }
 }