Bug 124620 Referenced Parameter icon should be invalid if the parameter in library is deleted
Description: Referenced parameter icon should be invalid if the source parameter in library is deleted. Steps to reproduce: 1.Create a library. Insert a report scalar parameter. 2.Create a report, use the above library. In the library explorer, pull the parameter to the data explorer view of report. 3.Open the library file, delete the parameter. Then reopen the report design file, the icon of parameter seems nothing happened. But if those operations happened in dataset, the icon of dataset in the report will be invalid. It is acceptable. Expected Result: The icon of referenced parameter should be invalid.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/DesignElementHandle.java
* Drops this element from the design. Removes the element from its
	 * container and name space, if any.
	 * <p>
	 * Note: If this element is referenceable, the property referring it will be
	 * unresolved.
	 * 
	 * @throws SemanticException
	 *             if this element has no container or the element cannot be
	 *             dropped.
	 * @see SlotHandle
	 * @see #dropAndClear()
	 */
	public void drop( ) throws SemanticException
	{
		DesignElement element = getElement( );
		DesignElement container = element.getContainer( );
		if ( container == null )
			throw new ContentException( element, -1,
					ContentException.DESIGN_EXCEPTION_HAS_NO_CONTAINER );
		int slotID = element.getContainerSlot( );
		assert slotID != -1;
		ContentCommand cmd = new ContentCommand( module, container );
		cmd.remove( element, slotID, true );
	}
	/**
	 * Finds the slot within this element that contains the given element.
	 * 
	 * @param content
	 *            handle to the content element to find
	 * @return The ID of the slot that contains the element, or