RFR: 8333569: jpackage tests must run app launchers with retries on Linux only

[Alexey Semenyuk]

Run app launchers in jpackage tests with retries on Linux only. Run them without retries on other platforms.

Supplementary remove `HelloApp.AppOutputVerifier.removePathEnvVar()` function. It sets an unused member field and is a leftover from [JDK-8347300](https://bugs.openjdk.org/browse/JDK-8347300) fix. This change has no functional impact; it cleans unused code.

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Commit messages:
 - 8333569: jpackage tests must run app launchers with retries on Linux only

Changes: https://git.openjdk.org/jdk/pull/23454/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23454&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8333569
  Stats: 42 lines in 3 files changed: 15 ins; 18 del; 9 mod
  Patch: https://git.openjdk.org/jdk/pull/23454.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23454/head:pull/23454

PR: https://git.openjdk.org/jdk/pull/23454