Bug 154828 Item from library contant user properties can't delete
Details: Item from library contant user properties can't delete Step: 1.New a library. 2.Add a label and add a user properites. 3.Public the library. 4.New a report design and use the library 5.Drop the label from library explorer into layout. 6.Try to delete it. Actual result: The label from library contant user properties can't be delete. Exception reuslt: The label can be delete.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/command/ContentCommand.java
* @throws UserPropertyException
	 *             if an error occurs, but the operation should not fail under
	 *             normal conditions
	 */
	private void dropUserProperties( DesignElement obj )
			throws UserPropertyException
	{
		Collection props = obj.getUserProperties( );
		if ( props != null )
		{
			UserPropertyCommand propCmd = new UserPropertyCommand( module, obj );
			Iterator iter = props.iterator( );
			while ( iter.hasNext( ) )
			{
				UserPropertyDefn prop = (UserPropertyDefn) iter.next( );
				propCmd.dropUserProperty( prop.getName( ) );
			}
		}
	}
	/**
	 * Removes all the contents of the element. Removes all contents from all
	 * slots. Does the drop recursively.
	 * 
	 * @param obj
	 *            the element to clean up
	 * @throws SemanticException
	 *             if an error occurs, but the operation should not fail under
	 *             normal conditions
	 */
	private void removeContents( DesignElement obj ) throws SemanticException