RFR: 8328541: Remove or update obsolete comment in JRootPane

[Prasanta Sadhukhan]

There is an old obsolete comment in JRootPane that is between the main documentation comment for the class and the declaration of the class itself which is  causing interference with the work to support Markdown in documentation comments using the `///` style of comment. (JEP 467) so removing this comment..

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Commit messages:
 - 8328541: Remove or update obsolete comment in JRootPane

Changes: https://git.openjdk.org/jdk/pull/18545/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18545&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8328541
  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/18545.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18545/head:pull/18545

PR: https://git.openjdk.org/jdk/pull/18545