core: Remove event subscriptions from monitored tasks

Removes Add/RemoveEventSubscriptions from monitored tasks
due to theirs simplicity.

Change-Id: I9bfa009a9193d3e7f18b2ba22e9d80502228a324
Bug-Url: https://bugzilla.redhat.com/919045
Signed-off-by: Martin Perina <mperina@redhat.com>