RFR(XS) 8055236: Deadlock during NMT2 shutdown on Windows

[Zhengyu Gu]

The problem is caused by acquiring locks inside MemTracker::shutdown(), 
which could be held by threads that have been already killed.

Given the MemTracker::shutdown() call is on JVM exiting path, the call 
is not necessary, should be removed.


Bug: https://bugs.openjdk.java.net/browse/JDK-8055236
Webrev: http://cr.openjdk.java.net/~zgu/8055236/webrev.00/ 
<http://cr.openjdk.java.net/%7Ezgu/8055236/webrev.00/>


Test:
    Tested on Windows x64 with following tests:
      nsk/jvmti/scenarios/allocation
      runtime/ParallelClassLoading


Thanks,

-Zhengyu