Revert "Reliably stop check() thread on exit."

It seems some platforms implementation of pthread_cond_timedwait() is
not that good enough and using pthread_cond_timedwait() instead of
nanosleep increased response times a lot.

This reverts commits r8525 and r8551.

Thanks to wimpie007 for the report and testing.

http://www.streamboard.tv/wbb2/thread.php?postid=457430

git-svn-id: http://streamboard.de.vu/svn/oscam/trunk@8552 4b0bc96b-bc66-0410-9d44-ebda105a78c1