RFR: 8342082: Remove unused BasicProgressBarUI.Animator.interval

[Andrey Turbanov]

The field `javax.swing.plaf.basic.BasicProgressBarUI.Animator.interval` is unused and can be removed.

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Commit messages:
 - [PATCH] Remove unused javax.swing.plaf.basic.BasicProgressBarUI.Animator.interval

Changes: https://git.openjdk.org/jdk/pull/21132/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21132&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8342082
  Stats: 3 lines in 1 file changed: 0 ins; 2 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/21132.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21132/head:pull/21132

PR: https://git.openjdk.org/jdk/pull/21132