RFR: JDK-8302385: Remove MetaspaceReclaimPolicy=none

[Thomas Stuefe]

This patch removes the "MetaspaceReclaimPolicy=none" mode. It had been a safety measure when JEP-387 came out, but it has never really been needed. Since it adds complexity (especially in tests) I'd like to get rid of it.

For more details, please see the reasoning in CSR [JDK-8302130](https://bugs.openjdk.org/browse/JDK-8302130).

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Tests:
- I manually ran metaspace tests (see test group "hotspot_metaspace") on linux x64 (release, fastdebug) and x86 (fastdebug) 
- GHAs are scheduled.

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Reviewer hint:

Removing the "none" Policy basically hardcodes the behavioral settings to:

Settings::**uncommit_free_chunks** => **true**; (as in, we always do reclaim upon classloader death)
Settings::**new_chunks_are_fully_committed** => **false**; (as in, newly allocated chunks are only committed as far as needed)

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Commit messages:
 - Remove MetaspaceReclaimPolicy=none

Changes: https://git.openjdk.org/jdk/pull/12554/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12554&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8302385
  Stats: 287 lines in 19 files changed: 35 ins; 189 del; 63 mod
  Patch: https://git.openjdk.org/jdk/pull/12554.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12554/head:pull/12554

PR: https://git.openjdk.org/jdk/pull/12554