RFR: 8246202: ChoiceBoxSkin: misbehavior on switching skin, part 2

[Jeanette Winzenburg]

issue is a listener in ChoiceBoxSkin that wasn't removed (forgotten in my first cleanup ;)

Removed, un-ignored test that failed/passed before/after the fix

-------------

Commit messages:
 - 8246202: ChoiceBoxSkin: misbehavior on switching skin, part 2

Changes: https://git.openjdk.java.net/jfx/pull/320/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=320&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8246202
  Stats: 5 lines in 2 files changed: 3 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jfx/pull/320.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/320/head:pull/320

PR: https://git.openjdk.java.net/jfx/pull/320