[lworld] RFR: Reduce excessive testing in SerializedObjectCombo test.

[Roger Riggs]

Drop the option to exhaustively test all combinations to reduce timeouts.

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Commit messages:
 - Reduce excessive testing in SerializedObjectCombo test.

Changes: https://git.openjdk.org/valhalla/pull/1299/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1299&range=00
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/valhalla/pull/1299.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1299/head:pull/1299

PR: https://git.openjdk.org/valhalla/pull/1299