RFR: 8372324: jdk/jfr/event/gc/detailed/TestStringDeduplicationEvent.java#Parallel failed

[Francesco Andreuzzi]

The assertion is used to validate a precondition for the test. As long as the deduplication happens inside the `RecordingStream` scope, a `StringDeduplication ` event will be recorded. Thus the assertion is not needed and can be removed.

-------------

Commit messages:
 - volatile
 - remove

Changes: https://git.openjdk.org/jdk/pull/28467/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28467&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8372324
  Stats: 6 lines in 1 file changed: 3 ins; 1 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/28467.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28467/head:pull/28467

PR: https://git.openjdk.org/jdk/pull/28467