RFR: 8284613: invalid use of @serial tag

[Alisen Chung]

Removed serial tag in method documentation

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Commit messages:
 - removed serial tag in methods that were causing warnings

Changes: https://git.openjdk.java.net/jdk/pull/8432/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8432&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8284613
  Stats: 12 lines in 12 files changed: 0 ins; 2 del; 10 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8432.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8432/head:pull/8432

PR: https://git.openjdk.java.net/jdk/pull/8432