8.0-b73: Creating and removing TreeView with static TreeItems leaks memory

Creating and removing TreeView with static TreeItems leaks memory.
The issue started to appear from build 8.0-b73, no issue in previous
build 8.0-b72.

Steps to reproduce:
> java -Xmx64m -cp "JFX_ROOT/rt/lib/jfxrt.jar" TreeViewMemTest -mode static

No memory leak in case new TreeItem instances are created on each pulse:
> java -Xmx64m -cp "JFX_ROOT/rt/lib/jfxrt.jar" TreeViewMemTest -mode dynamic


The memory leak happens because TreeViews objects are not deleted.
The references to them are hold from
 staticTreeRoot -> expanded -> helper -> invalidationListeners

To see more details run the test with -XX:+HeapDumpOnOutOfMemoryError and
then analyze hprof file (you can use Eclipse memory analyzer for example).