RFR: 8255577: Possible issues with SR_initialize

[David Holmes]

Please review this trivial change that:

1. Removed dead code in relation to SR_sigset (unused since JDK 6)
2. Modified a vague comment to be slightly less vague.
3. Correct the copyright header which had been broken first in 2021 then again in 2022.

Testing: local test build.

Thanks,
David

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Commit messages:
 - 8255577: Possible issues with SR_initialize

Changes: https://git.openjdk.java.net/jdk/pull/7584/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7584&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8255577
  Stats: 7 lines in 1 file changed: 0 ins; 5 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7584.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7584/head:pull/7584

PR: https://git.openjdk.java.net/jdk/pull/7584