RFR: 8233029: Obsolete flag GCTaskTimeStampEntries

[Leo Korinth]

Hi,

When I changed ParallelGC to use WorkGangs instead of GCTasks, I 
unfortunately missed to remove (thereafter unused) command line option 
GCTaskTimeStampEntries. Here is a fix for that.

CSR:
https://bugs.openjdk.java.net/browse/JDK-8234396

Bug:
https://bugs.openjdk.java.net/browse/JDK-8233029

Webrev:
http://cr.openjdk.java.net/~lkorinth/8233029/00

Testing:
tier 1-3

Thanks,
Leo