RFR: 8275767: JDK source code contains redundant boolean operations in jdk.charsets

[Naoto Sato]

Trivial clean-up.

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Commit messages:
 - 8275767: JDK source code contains redundant boolean operations in jdk.charsets

Changes: https://git.openjdk.java.net/jdk/pull/6110/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6110&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8275767
  Stats: 2 lines in 2 files changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6110.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6110/head:pull/6110

PR: https://git.openjdk.java.net/jdk/pull/6110