[jdk17u-dev] RFR: 8286663: Resolve IDE warnings in WTrayIconPeer and SystemTray

[Goetz Lindenmaier]

I backport this for parity with 17.0.6-oracle.

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Commit messages:
 - Backport a9b9831f2a88ed3b7701d402b167a096b94aeb98

Changes: https://git.openjdk.org/jdk17u-dev/pull/737/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=737&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8286663
  Stats: 33 lines in 2 files changed: 8 ins; 14 del; 11 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/737.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev pull/737/head:pull/737

PR: https://git.openjdk.org/jdk17u-dev/pull/737