RFR: 8301822: BasicLookAndFeel does not need to check for null after checking for type

[SWinxy]

BasicLookAndFeel checks an instanceof in its `AWTEventHelper` listener class, but the result of that will always be non-null. The check should be removed.

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Commit messages:
 - BasicLookAndFeel does not need to check for null after checking for type

Changes: https://git.openjdk.org/jdk/pull/12019/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12019&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301822
  Stats: 17 lines in 1 file changed: 2 ins; 5 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/12019.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12019/head:pull/12019

PR: https://git.openjdk.org/jdk/pull/12019