RFR: 8309909: remove test nsk.jvmti test objmonusage006 from ProblemList-Virtual.txt

[Serguei Spitsyn]

The following bug was closed as "Cannot Reproduce":
[8300709](https://bugs.openjdk.org/browse/JDK-8300709) nsk/jvmti/GetObjectMonitorUsage/objmonusage006 test asserts with virtual thread wrapper

I was not able to reproduce the assert in thousands mach5 runs on multiple debug builds.
Also, the original sources were significantly changed, so it is not clear anymore in what context the assert was fired.
The test is problem-listed in `ProblemList-Virtual.txt`.

This sub-task is to unproblem-list the test:
   `vmTestbase/nsk/jvmti/GetObjectMonitorUsage/objmonusage006/TestDescription.java`
 
If the original asset is reproduced again then the plan is to reopen the [8300709](https://bugs.openjdk.org/browse/JDK-8300709) and update it with the details needed for issue investigation.

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Commit messages:
 - 8309909: remove test nsk.jvmti test objmonusage006 from ProblemList-Virtual.txt

Changes: https://git.openjdk.org/jdk/pull/14610/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14610&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8309909
  Stats: 4 lines in 1 file changed: 0 ins; 4 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/14610.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14610/head:pull/14610

PR: https://git.openjdk.org/jdk/pull/14610