RFR: 8292280: Unused field 'keyListener' in BasicRadioButtonUI

[Andrey Turbanov]

Field `keyListener` was added under [JDK-8033699](https://bugs.openjdk.org/browse/JDK-8033699). But then all its usages were removed in [JDK-8249548](https://bugs.openjdk.org/browse/JDK-8249548)

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Commit messages:
 - [PATCH] Unused field 'keyListener' in BasicRadioButtonUI

Changes: https://git.openjdk.org/jdk/pull/9832/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9832&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292280
  Stats: 10 lines in 1 file changed: 0 ins; 9 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/9832.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9832/head:pull/9832

PR: https://git.openjdk.org/jdk/pull/9832