RFR: 8292206: TestCgroupMetrics.java fails as getMemoryUsage() is lower than expected

[Ioi Lam]

The `testMemoryUsage()` test scenario queries the total memory usage of all processes of the current Linux user, including other concurrently running jtreg test cases. Even if the current process allocates 256MB of ram, it's possible for other dying processes to release much more than that amount. Therefore, it's not possible to guarantee that `Metrics.getMemoryUsage()` would return a higher number.

I am removing this test scenario for now as I don't see it providing any actual value.

If we want to have more in-depth functional tests for the `Metrics.getMemoryXXX()` APIs, we need to do it inside a container in a more controlled setting.

-------------

Commit messages:
 - 8292206: TestCgroupMetrics.java fails as getMemoryUsage() is lower than expected

Changes: https://git.openjdk.org/jdk/pull/11734/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11734&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292206
  Stats: 54 lines in 4 files changed: 0 ins; 54 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/11734.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11734/head:pull/11734

PR: https://git.openjdk.org/jdk/pull/11734