[cleanup] Remove unused internal class DesignerPropertySourceAdapter 

Change-Id: Ib6d2e56e28abba2cf71c3a49cf34bda59881c593
Signed-off-by: Pierre-Charles David <pierre-charles.david@obeo.fr>
[cleanup] Remove unused internal class OpenedSessionTab 

Change-Id: Id1d6c3e93cb7de501663534d1444ac2f2c766a8d
Signed-off-by: Pierre-Charles David <pierre-charles.david@obeo.fr>