Cleanup dead code

After the hardening exercises, there are few places in preemption.go which we are seeing dead code, doubtful of going through any situations. Need to assess those places by reviewing and/or writing appropriate test cases. Below link is one of such places which had come through reviews:

https://github.com/apache/yunikorn-core/pull/830#discussion_r1636755074

In case if we find those code to be dead, it needs to be cleaned up.