How to remove suggestions for a input field?
Take a look at hook_form_alter. Also refer to the drupal FAPI, there are many form controls are available which you can use in a form.

For your case, below example will be helpful.

function example_form_alter(&amp;$form, &amp;$form_state, $form_id) {
  if($form_id === 'your_form_id'){
     $form['your_field']['#attributes'] = array('autocomplete' =&gt; 'Off');
  }
}


Other option is with JS.

Drupal.behaviors.exampleModule = {
  attach: function (context, settings) {
    $('input[type="text"]').each(function (i, input) {
      $(input).attr('autocomplete', 'off);
    });
  }
};