Fix race condition in UidRecord cleanup

It's a situation that:
1) An app process is killed;
2) A new instance of this process is created right after it
3) The bindeDied handling happens after 2)

During 2), while creating the new ProcessRecord, the old ProcessRecord
will be removed and this makes the total num of processes in this
UidRecord to be 0, then the new ProcessRecord will bump that number
by 1, in the meanwhile the new ProcessRecord will be kept in the
process name map,
During 3), while doing the cleanup for old ProcessRecord, it tries to
remove itself from the process name map, which actually has the
new ProcessRecord, so the total num of processes in the UidRecord
will become 0.

Now the fix is to make sure we are cleaning up the right ProcessRecord,
so in step 3) we will see it's already cleaned, thus we won't mess up
with the UidRecord.

Bug: 161466248
Test: see b/161466248#comment17 for detailed test steps
Change-Id: I2685e3f0162098b9b95f6b248b67aeb498e50c8e