[jdk21u-dev] RFR: 8339524: Clean up a few ExtendedRobot tests

[Goetz Lindenmaier]

I backport this for parity with 21.0.7-oracle

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Commit messages:
 - Backport 16232578d9acf9d0b5a9ad0e7530291471b5cc9c

Changes: https://git.openjdk.org/jdk21u-dev/pull/1304/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=1304&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8339524
  Stats: 60 lines in 1 file changed: 13 ins; 30 del; 17 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/1304.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/1304/head:pull/1304

PR: https://git.openjdk.org/jdk21u-dev/pull/1304