RFR: 8347428: Avoid using secret-key in specifications

[Ben Perez]

There are quite some places in API specifications that use the term "secret-key". This is not a formal term. Consider replacing them with "secret key".

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Commit messages:
 - removed all instances of  in docs/comments

Changes: https://git.openjdk.org/jdk/pull/23342/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23342&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8347428
  Stats: 22 lines in 6 files changed: 0 ins; 0 del; 22 mod
  Patch: https://git.openjdk.org/jdk/pull/23342.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23342/head:pull/23342

PR: https://git.openjdk.org/jdk/pull/23342