Bug 158778 [Viewers] request for remove(parent, index) API on tree viewer
3.3 It would be helpful to have a 'remove(Object parent, int index)' method on the tree viewer to complement that 'replace(...)' and 'setChildCount(...)' APIs. The debug platform requires such a method to implement filtering in virtual tree views. Rather than performing a 'replace/remove' based on elements, the content provider can make one atomic call to remove an element at a specific index.
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/AbstractTreeViewer.java
/**
	 * Returns the item before the given item in the tree, or <code>null</code>
	 * if there is no previous item.
	 * 
	 * @param item
	 *            the item
	 * @return the previous item, or <code>null</code> if none
	 */
	protected Item getPreviousItem(Item item) {
		
		
		Item parent = getParentItem(item);
		if (parent == null) {
			return null;
		}
		Item[] siblings = getItems(parent);
		if (siblings.length == 0 || siblings[0] == item) {
			return parent;
		}
		Item previous = siblings[0];
		for (int i = 1; i < siblings.length; i++) {
			if (siblings[i] == item) {
				return rightMostVisibleDescendent(previous);
			}
			previous = siblings[i];
		}
		return null;
	}
	
	protected Object[] getRawChildren(Object parentElementOrTreePath) {