RFR: 8303253: Remove unnecessary calls to super() in java.time value based classes

[Roger Riggs]

To simplify future work changing some java.time value based classes to Valhalla value classes, the explicit calls to super() are removed from Duration, Instant, and ZoneOffset.

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Commit messages:
 - 8303253: Remove unnecessary calls to super() in java.time value based classes

Changes: https://git.openjdk.org/jdk/pull/12771/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12771&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303253
  Stats: 6 lines in 3 files changed: 0 ins; 3 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/12771.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12771/head:pull/12771

PR: https://git.openjdk.org/jdk/pull/12771