Remove form elements with ajax
It's actually easier than you think :)

You can access a $form_state['triggering_element'] in your ajax callback function.

Something like this:


function my_ajax_callback($form, $form_state) {
  $ps = &$form_state['triggering_element']['#parents'];
  $k = $ps[2]; // field collection row number 
  $collection = $form[$ps[0]][$ps[1]][$ps[2]];
  $element = $ps[3];
  ...


that was the snippet to access a changed textfield inside a field collection with multiple rows. Just adopt it for your particular form structure.