RFR: 8344578: Clean up left over java.security and sun.security imports in Swing classes

[Phil Race]

This cleans up some left over un-used imports and one variable that was left behind.

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Commit messages:
 - 8344578

Changes: https://git.openjdk.org/jdk/pull/22260/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22260&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8344578
  Stats: 12 lines in 4 files changed: 0 ins; 12 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/22260.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22260/head:pull/22260

PR: https://git.openjdk.org/jdk/pull/22260