core: remove redundant synchronization (CoCo cleanup)

a method which is executed by our quartz in fixed delay can only be
executed by one thread at each given time, because before executing
it we remove it from the quartz pool and when it ends we put it back.
so no need to synchronize anything for protecting from parallel
executions of the same critical section

Change-Id: I588de14e21f19ef59781b382b2450b8723635667
Signed-off-by: Arik Hadas <ahadas@redhat.com>