[jdk21u-dev] RFR: 8359207: Remove runtime/signal/TestSigusr2.java since it is always skipped

[SendaoYan]

Hi all,

This pull request contains a backport of commit [51877f56](https://github.com/openjdk/jdk/commit/51877f568ba84a8ec7721656571c90c5eb952eb3) from the [openjdk/jdk](https://git.openjdk.org/jdk) repository.

The commit being backported was authored by SendaoYan on 17 Jun 2025 and was reviewed by Daniel D. Daugherty and David Holmes.

Thanks!

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Commit messages:
 - Backport 51877f568ba84a8ec7721656571c90c5eb952eb3

Changes: https://git.openjdk.org/jdk21u-dev/pull/2106/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=2106&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8359207
  Stats: 43 lines in 2 files changed: 0 ins; 41 del; 2 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/2106.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/2106/head:pull/2106

PR: https://git.openjdk.org/jdk21u-dev/pull/2106