RFR: 8328820: Remove unused imports in javafx.swing

[Andy Goryachev]

Removed unused imports in javafx.swing (1 change) module.

See the discussion in [JDK-8289379](https://bugs.openjdk.org/browse/JDK-8289379)

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Commit messages:
 - 8328820: Remove unused imports in javafx.swing

Changes: https://git.openjdk.org/jfx/pull/1428/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1428&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8328820
  Stats: 17 lines in 1 file changed: 7 ins; 9 del; 1 mod
  Patch: https://git.openjdk.org/jfx/pull/1428.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1428/head:pull/1428

PR: https://git.openjdk.org/jfx/pull/1428