Fix race conditions in removing dying process record

While waiting for the death of a process, if its subsequent process
record is created and killed immediately, we may end up removing
the former process record from the dying process list.

Bug: 201305599
Bug: 206336727
Test: Presubmit
Change-Id: I00521a5561d98f2df6f52443b9e23025faeaeb3c