RFR: 8285360: [TestBug] Cleanup a few ignored javafx.controls unit tests

[Ajit Ghaisas]

This PR is to cleanup a few `javafx.controls` unit tests that were ignored. 

Here is the list of targeted unit test classes- 
- Ignored tests re-enabled and fixed - `DateCellTest`, `CellTest`, `PaginationTest`
- Ignored tests removed -  `RadioMenuItemTest`, `PopupControlTest`

Results of `javafx.controls` unit tests-
**Before this PR :** 
Total tests - 8610
Failures - 0
Ignored - 246

**After this PR :** 
Total tests - 8608
Failures - 0
Ignored - 235

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

Commit messages:
 - fix or remove ignored unit tests

Changes: https://git.openjdk.java.net/jfx/pull/780/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=780&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8285360
  Stats: 49 lines in 5 files changed: 24 ins; 24 del; 1 mod
  Patch: https://git.openjdk.java.net/jfx/pull/780.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/780/head:pull/780

PR: https://git.openjdk.java.net/jfx/pull/780