RFR: JDK-8310550: Adjust references to rt.jar

[Matthias Baesken]

There are a few references to rt.jar in comments and in the codebase itself. Some of them might be removed or adjusted.

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Commit messages:
 - JDK-8310550

Changes: https://git.openjdk.org/jdk/pull/14593/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14593&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8310550
  Stats: 14 lines in 12 files changed: 0 ins; 7 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/14593.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14593/head:pull/14593

PR: https://git.openjdk.org/jdk/pull/14593