RFR: 8307448: Test RedefineSharedClassJFR fail due to wrong assumption

[Stefan Johansson]

Please review this fix to avoid a tier1 test failure.

**Summary**
The newly added test wrongfully assumed that one of the transformed classes would be in use. This seem to be the case in most runs, but there is no guarantee. This change fixes the test to only verify that nothing is seen as shared when running with -Xshare:off.

**Testing**
Verified that the test still passes locally.

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Commit messages:
 - Updated comment
 - 8307448: Test RedefineSharedClassJFR fail due to wrong assumption

Changes: https://git.openjdk.org/jdk/pull/13801/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13801&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8307448
  Stats: 10 lines in 1 file changed: 1 ins; 3 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/13801.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13801/head:pull/13801

PR: https://git.openjdk.org/jdk/pull/13801