Bug 121498 When datasource/dataset deleted, the datasource/dataset property binding element haven't been deleted
When deleted the datasource/dataset, the datasource/dataset property binding element haven't been deleted. Expected result: This operation must be a transaction.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/DesignElementHandle.java
*             If the property is not found.
	 */
	public void dropUserPropertyDefn( String propName )
			throws UserPropertyException
	{
		DesignElement element = getElement( );
		UserPropertyCommand cmd = new UserPropertyCommand( module, element );
		cmd.dropUserProperty( propName );
	}
	/**
	 * Returns a handle to the element that this element extends.
	 * 
	 * @return the parent element. Returns <code>null</code> if this element
	 *         does not have a parent, or if the extends name does not resolve
	 *         to a valid element.
	 */
	public DesignElementHandle getExtends( )
	{
		DesignElement parent = getElement( ).getExtendsElement( );
		if ( parent == null )
			return null;
		return parent.getHandle( module );
	}
	/**
	 * Sets this element to extend the given element.
	 * 
	 * @param parent
	 *            handle to the element that this element is to extend. If
	 *            <code>null</code>, then this element will no longer extend
	 *            another element.