RFR: 8344914: OOME in several tests since JDK-6672644 - JComboBox still scrolling

[Damon Nguyen]

Backout for https://github.com/openjdk/jdk/pull/20845. Removes additions to `BasicScrollBarUI` and removes the test `JComboBoxScrollFocusTest`. Original PR caused some tests to fail that indicate a memory leak.

Ran against clientlibs job, and all relevant tests pass (including the few tests that were failing from the original PR).

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Commit messages:
 - Initial commit for backout

Changes: https://git.openjdk.org/jdk/pull/22346/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=22346&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8344914
  Stats: 120 lines in 2 files changed: 0 ins; 120 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/22346.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/22346/head:pull/22346

PR: https://git.openjdk.org/jdk/pull/22346