The following JavaScript function should do the trick.
You need JQuery to make it work.
dropdown_remove_repeated: function () {
var $selects = $('select');
$selects.each(function () {
var $select = $(this);
var $options = $select.find('option');
$options.each(function () {
var $option = $(this);
$option.siblings().each(function () {
var $this = $(this);
if ($this.text().trim() === $option.text().trim()) {
$this.remove();
}
});
});
});
}
var $selects = $('select');
$selects.each(function () {
var $select = $(this);
var $options = $select.find('option');
$options.each(function () {
var $option = $(this);
$option.siblings().each(function () {
var $this = $(this);
if ($this.text().trim() === $option.text().trim()) {
$this.remove();
}
});
});
});
}