RFR: 8359207: Remove redundant runtime/signal/TestSigusr2.java

[SendaoYan]

Hi all,

The test `runtime/signal/TestSigusr2.java` has jtreg tag `@requires os.family != "windows" & os.family != "aix"`, and this test will skip on linux and macos. Thus this test will is always skipped indeed. So I want to removed this test. Test-fix only, no rsik.

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Commit messages:
 - 8359207: Remove redundant runtime/signal/TestSigusr2.java

Changes: https://git.openjdk.org/jdk/pull/25825/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25825&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/jdk/pull/25825.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25825/head:pull/25825

PR: https://git.openjdk.org/jdk/pull/25825