<Swing Dev> RFR: 8260035: Deproblemlist few problemlisted test

[Prasanta Sadhukhan]

Few problemlisted test
javax/swing/plaf/basic/Test6984643.java
javax/swing/JMenuItem/6249972/bug6249972.java
javax/swing/JTree/6263446/bug6263446.java
were unstable in mach5 nightly testing. These can be deproblemlisted now with appropriate stability fixes. 
Mach5 jobs running for several iterations for all these tests in all platforms is ok. Link in JBS.

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Commit messages:
 - 8260035: Deproblemlist few problemlisted test

Changes: https://git.openjdk.java.net/jdk/pull/2161/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2161&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8260035
  Stats: 114 lines in 4 files changed: 29 ins; 9 del; 76 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2161.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2161/head:pull/2161

PR: https://git.openjdk.java.net/jdk/pull/2161