RFR: 8261728: SimpleDateFormat should link to DateTimeFormatter

[Naoto Sato]

Please review this simple doc fix. A CSR will be filed accordingly.

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Commit messages:
 - 8261728: SimpleDateFormat should link to DateTimeFormatter

Changes: https://git.openjdk.java.net/jdk/pull/2616/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2616&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8261728
  Stats: 8 lines in 2 files changed: 4 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2616.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2616/head:pull/2616

PR: https://git.openjdk.java.net/jdk/pull/2616