Trigger event thread only if we need execute process

Trigger event thread only if we need execute process

Sometimes, Canceled running task can wake up main thread.
This logic might crush some toolkit UTC.
And also it is useless.

We already have some logics to avoid too-much-cached cancel
tasks. So now we don't need to trigger event thread for
canceled tasks, and flush.

Change-Id: Ib4a62757260cc459941f8e153e37eab70f5f885a
Signed-off-by: Eunki Hong <eunkiki.hong@samsung.com>