RFR: 8245634: [TestBug] Enable and fix tests ignored with message "impl_cssSet API removed"

[Ajit Ghaisas]

This is a simple test fix.

Issue : https://bugs.openjdk.java.net/browse/JDK-8245634

After fixing [JDK-8245457,](https://bugs.openjdk.java.net/browse/JDK-8245457) I found that there are more ignored tests
of similar nature that can be enabled and fixed. A search for ignored tests with message "impl_cssSet API removed" -
revealed a total 6 occurrences in 4 files - 1) CellTest
2) CheckBoxTest
3) ChoiceBoxTest
4) DateCellTest

This PR enables and fixes these tests.

-------------

Commit messages:
 - enable ignored unit tests

Changes: https://git.openjdk.java.net/jfx/pull/239/files
 Webrev: https://webrevs.openjdk.java.net/jfx/239/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8245634
  Stats: 65 lines in 4 files changed: 48 ins; 7 del; 10 mod
  Patch: https://git.openjdk.java.net/jfx/pull/239.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/239/head:pull/239

PR: https://git.openjdk.java.net/jfx/pull/239