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
slotHandle.dropAndClear( i );
		}
	}
	/**
	 * Removes an existing user property definition from the element. This
	 * method will remove all existing values for the property, in both this
	 * element and all its derived elements.
	 * 
	 * @param propName
	 *            the name of the user property to remove
	 * @throws UserPropertyException
	 *             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( );