foreach (Adorner adorner in al.GetAdorners(this.BlockListbox))
{
    if (adorner is BlockConnectorAdorner)
    {
	var bca = adorner as BlockConnectorAdorner;

	if (bca.BlockConnector.TargetVariableControl == bc.TargetVariableControl)
	    al.Remove(bca);
    }
}

#############################################

var q = from adorner in al.GetAdorners(this.BlockListbox)
	 where (adorner is BlockConnectorAdorner)
	 && ((adorner as BlockConnectorAdorner).BlockConnector.TargetVariableControl == bc.TargetVariableControl)
	 select adorner;

foreach (Adorner a in q)
{
    al.Remove(a);
}