RFR: 8255497: [TestBug] Controls unit tests - clean up unnecessary prints on STANDARD_OUT

[Ajit Ghaisas]

This is a test cleanup task. More details in the JBS.

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Commit messages:
 - clear_stdout_prints

Changes: https://git.openjdk.java.net/jfx/pull/341/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=341&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8255497
  Stats: 35 lines in 8 files changed: 2 ins; 15 del; 18 mod
  Patch: https://git.openjdk.java.net/jfx/pull/341.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/341/head:pull/341

PR: https://git.openjdk.java.net/jfx/pull/341