Icons created in FilteredTree are never accessed. Most likely a
remainder of the days in which windows did not support ICONS cancel.

Change-Id: Ia4cec37f1a3bc7b6cec07af92d741cf369cee3f4
Signed-off-by: Lars Vogel <Lars.Vogel@vogella.com>
Reviewed-on: https://git.eclipse.org/r/c/platform/eclipse.platform.ui/+/187268
Tested-by: Platform Bot <platform-bot@eclipse.org>