RFR: 8295715: Minimize disabled warnings in serviceability libs

[Magnus Ihse Bursie]

After [JDK-8294281](https://bugs.openjdk.org/browse/JDK-8294281), it is now possible to disable warnings for individual files instead for whole libraries. I used this opportunity to go through all disabled warnings in the serviceability native libraries.

Any warnings that were only triggered in a few files were removed from the library as a whole, and changed to be only disabled for those files.

Some warnings didn't trigger in any file anymore, and could just be removed.

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Commit messages:
 - 8295715: Minimize disabled warnings in serviceability libs

Changes: https://git.openjdk.org/jdk/pull/10786/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10786&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8295715
  Stats: 16 lines in 4 files changed: 4 ins; 2 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/10786.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10786/head:pull/10786

PR: https://git.openjdk.org/jdk/pull/10786