core: remove unneeded setSucceeded

The following code in the started thread is executed after the tasks
were cleared, therefore there's no need to execute setSucceeded,
furthermore, as the class isn't thread safe it's risky to have that call
in terms of future changes.

Change-Id: I2d15162aded39cf43064b14fd6c02644bf95936f
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1138124
Signed-off-by: Liron Aravot <laravot@redhat.com>