RFR: JDK-8267434: Remove LinkOutput[Impl]

[Jonathan Gibbons]

Please review a trivial patch to remote an unused internal interface and its implementation.

I've looked as far back as JDK 8, and the code was unused even back then.

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Commit messages:
 - JDK-8267434: Remove LinkOutput[Impl]

Changes: https://git.openjdk.java.net/jdk/pull/4121/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4121&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267434
  Stats: 120 lines in 2 files changed: 0 ins; 120 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4121.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4121/head:pull/4121

PR: https://git.openjdk.java.net/jdk/pull/4121