RFR: 8234540: javafx.web LeakTest.testGarbageCollectability fails intermittently

[Arun Joseph]

Cause: The test assumes that WebView/WebPage will be GCed right after `System.gc()`

Fix: Use `runFinalization()` and `sleep()` to wait for objects to get GCed

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

Commit messages:
 - Update copyright year
 - Remove unwanted line
 - 8234540: javafx.web LeakTest.testGarbageCollectability fails intermittently

Changes: https://git.openjdk.java.net/jfx/pull/236/files
 Webrev: https://webrevs.openjdk.java.net/jfx/236/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8234540
  Stats: 33 lines in 1 file changed: 7 ins; 15 del; 11 mod
  Patch: https://git.openjdk.java.net/jfx/pull/236.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/236/head:pull/236

PR: https://git.openjdk.java.net/jfx/pull/236