Currently, social activities aren't deleted when the source asset is
deleted. Deleting is triggered only when the Social Activity
is interpreted for the Notification portlet and the source asset is
not found. However, the corresponding row is still shown in the
Notification portlet as "Activity no longer applies". By
refreshing the page this entry disappears, but this behavior can be
confusing. Additionally, deleting is done just for the specific user.
Notifications for the same asset for other users are kept intact.
How about changing this logic and deleting all related social
activities together with deleting the original asset? We basically
need a new service method deleting all activities for the given
classID and classPK and call it in delete method of *LocalServiceImpl class.
