RFR: 8274680: Remove unnecessary conversion to String in java.desktop

[Andrey Turbanov]

Cleanup unnecessary String.valueOf calls (and similar) when conversion will happen implicitly anyway

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Commit messages:
 - [PATCH] Remove unnecessary conversion to String in java.desktop

Changes: https://git.openjdk.java.net/jdk/pull/5799/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5799&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8274680
  Stats: 67 lines in 16 files changed: 0 ins; 18 del; 49 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5799.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5799/head:pull/5799

PR: https://git.openjdk.java.net/jdk/pull/5799