This removes following implementation methods in Scene by making them
package-scope. They were previously deprecated for removal by
[JDK-8270246](https://bugs.openjdk.java.net/browse/JDK-8270246):
public void disposePeer()
public void enableInputMethodEvents(boolean enable)
public void processKeyEvent(KeyEvent e)
One of the test harness classes was calling `Scene::processKeyEvent` directly,
so I changed it to call it via `SceneHelper`.
-------------
Commit messages:
- 8270839: Remove deprecated implementation methods from Scene
Changes: https://git.openjdk.java.net/jfx/pull/579/files
Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=579&range=00
Issue: https://bugs.openjdk.java.net/browse/JDK-8270839
Stats: 25 lines in 2 files changed: 2 ins; 17 del; 6 mod
Patch: https://git.openjdk.java.net/jfx/pull/579.diff
Fetch: git fetch https://git.openjdk.java.net/jfx pull/579/head:pull/579
PR: https://git.openjdk.java.net/jfx/pull/579
