Bug 182076 Delete a style from a report item doesn't affect report xml source
Steps to reproduce: 1.Insert a label onto layout; 2.New a style, suppose named it "NewStyle"; 3.Right click the label and on the drop down list, choose Style->Apply Style->NewStyle; 4.Save the report design; 5.Right click the label and on the drop down list, choose Style->Delete Style->NewStyle; 6.Save the report design; Expected result: NewStyle is deleted from report design, and the label doesn't have the style property. Actual result: Switch to report xml source, a error mark indicate that the label still has a style property:<property name="style">NewStyle</property>
UI/org.eclipse.birt.report.designer.core/src/org/eclipse/birt/report/designer/core/commands/DeleteCommand.java
* 
	 * @param model
	 *            the model
	 */
	public DeleteCommand( Object model )
	{
		this.model = model;
	}
	/**
	 * Executes the Command. This method should not be called if the Command is
	 * not executable.
	 */
	public void execute( )
	{
		if ( DesignerConstants.TRACING_COMMANDS )
		{
			System.out.println( "DeleteCommand >> Starts ... " ); 
		}
		try
		{
			dropSource( model );
			if ( !embeddedImageList.isEmpty( ) )
			{
				for ( int i = 0; i < embeddedImageList.size( ); i++ )
				{
					IStructure item = ( (EmbeddedImageHandle) embeddedImageList.get( i ) ).getStructure( );
					String name = ( (EmbeddedImageHandle) embeddedImageList.get( i ) ).getName( );
					SessionHandleAdapter.getInstance( )
							.getReportDesignHandle( )
							.getPropertyHandle( ReportDesignHandle.IMAGES_PROP )