Delete generated image sizes from image upload after Formidable form submission

functions.php

<?php

add_action('frm_after_create_entry', 'after_entry_created', 50, 2); //use 50 to make sure this is done very last
function after_entry_created($entry_id, $form_id){
  if($form_id == 8){ //change 5 to the ID of your form
    $field_id = 79; //change 25 to the ID of the upload field
    if(isset($_POST['item_meta'][$field_id])){
      if(is_array($_POST['item_meta'][$field_id])){
        foreach ($_POST['item_meta'][$field_id] as $p){
          if(is_numeric($p))
            $image_metadata = wp_get_attachment_metadata( $p );
            $image_sizes = $image_metadata['sizes'];
            $fullsizepath = get_attached_file($p);
            $upload_dir =  dirname( $fullsizepath ) . DIRECTORY_SEPARATOR;;
            foreach ($image_sizes as $image_size) {
                wp_delete_file( $upload_dir . $image_size['file'] );
            }
        }
      }else if(is_numeric($_POST['item_meta'][$field_id])){
        $image_metadata = wp_get_attachment_metadata( $_POST['item_meta'][$field_id] );
        $image_sizes = $image_metadata['sizes'];
        $fullsizepath = get_attached_file($_POST['item_meta'][$field_id]);
        $upload_dir =  dirname( $fullsizepath ) . DIRECTORY_SEPARATOR;;
        foreach ($image_sizes as $image_size) {
            wp_delete_file( $upload_dir . $image_size['file'] );
        }
      }
    }
  }
}