RFR: 8376992: Remove AppContext from SystemTray implementation

[Phil Race]

Remove AppContext from java/awt/SystemTray

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Commit messages:
 - 8376992

Changes: https://git.openjdk.org/jdk/pull/29531/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29531&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8376992
  Stats: 19 lines in 1 file changed: 4 ins; 14 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/29531.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29531/head:pull/29531

PR: https://git.openjdk.org/jdk/pull/29531