RFR: Reduce the number of new product flags

[Aleksey Shipilev]

Eventual upstreaming would require a CSR for every changed product flag. Not every flag we have now needs to be product, we can reduce them to be experimental.

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Commit messages:
 - Work

Changes: https://git.openjdk.org/shenandoah/pull/251/files
 Webrev: https://webrevs.openjdk.org/?repo=shenandoah&pr=251&range=00
  Stats: 6 lines in 1 file changed: 0 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/shenandoah/pull/251.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/251/head:pull/251

PR: https://git.openjdk.org/shenandoah/pull/251