RFR: 8328064: Remove obsolete comments in constantPool and metadataFactory

[Yude Lin]

Clean up some obsolete comments:
After 8243287, there is no longer the concept of "pseudo-string";
After 8072061, the "read_only" argument that the comment is referring to is removed.

Cheers

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Commit messages:
 - 8328064: Remove obsolete comments in constantPool and metadataFactory

Changes: https://git.openjdk.org/jdk/pull/18266/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18266&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8328064
  Stats: 3 lines in 2 files changed: 0 ins; 2 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/18266.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18266/head:pull/18266

PR: https://git.openjdk.org/jdk/pull/18266