RFR(s): 8042310: TestStringDeduplicationMemoryUsage test failing

[Per Liden]

Could I please have this patch reviewed.

Summary: This test is unstable and is failing intermittently in nightly 
testing. The test relies on getting the heap usage via an MXBean, but 
since the test doesn't have complete control over what ends up on the 
heap the heap usage is sometimes slightly higher than the test expects. 
There are other (stable) tests which already verifies than string 
deduplication actually happens when it's supposed to, so this test 
doesn't really add much value. This patch removes the unstable test 
completely.

Bug: https://bugs.openjdk.java.net/browse/JDK-8042310
Webrev: http://cr.openjdk.java.net/~pliden/8042310/webrev.0/

Thanks!
/Per