RFR: JDK-8314588: gc/metaspace/TestMetaspaceInitialization.java failed "assert(capacity_until_gc >= committed_bytes) failed: capacity_until_gc: 3145728 < committed_bytes: 3211264"

[Thomas Stuefe]

See JBS issue text and comments.

I remove the assert that tests that the metaspace commit size has to be >= the GC threshold and make sure we don't overflow the subtraction.

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Commit messages:
 - JDK-8314588-gc/metaspace/TestMetaspaceInitialization.java-failed-assert-capacity_until_gc-=-committed_bytes-failed-capacity_until_gc-3145728-committed_bytes-3211264

Changes: https://git.openjdk.org/jdk/pull/16216/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16216&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8314588
  Stats: 8 lines in 1 file changed: 3 ins; 4 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/16216.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16216/head:pull/16216

PR: https://git.openjdk.org/jdk/pull/16216