RFR: 8300540: Serial: Remove obsolete comments in GenMarkSweep

Wed Jan 18 14:40:57 UTC 2023

Trivial change of removing stale comments.

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Commit messages:
 - s1-remove-stale-comment

Changes: https://git.openjdk.org/jdk/pull/12074/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12074&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8300540
  Stats: 21 lines in 1 file changed: 0 ins; 19 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/12074.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12074/head:pull/12074

PR: https://git.openjdk.org/jdk/pull/12074