<Swing Dev> RFR: 8225045: javax/swing/JInternalFrame/8146321/JInternalFrameIconTest.java fails on linux-x64

[Prasanta Sadhukhan]

This test was failing on mach5 nightly on ubuntu systems long time back. Modified the test to add some delays and call robot.waitForIdle() to make it more stable and the resultant test passes on all mach5 systems including linux consisting of ubuntu 19.10, 18.04,20.10,20.04 so we can remove the test from problemlist.
mach5 job running for several iterations is posted in JBS.

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Commit messages:
 - 8225045: javax/swing/JInternalFrame/8146321/JInternalFrameIconTest.java fails on linux-x64

Changes: https://git.openjdk.java.net/jdk/pull/2003/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2003&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8225045
  Stats: 13 lines in 2 files changed: 11 ins; 1 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2003.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2003/head:pull/2003

PR: https://git.openjdk.java.net/jdk/pull/2003