How can I set the help text as an input placeholder on the user login form?
unset($form['pass']['#description']);


or

hide($form['pass']['#description']);


is probably sufficient for the description element. I wouldn't use both above on form fields/controls though, because that may lead to unwanted validation errors and so forth.



$form['name']['#description']['#access'] = FALSE;


does not work for 'description' element as it is not a form control(field).

If anybody knows of better ways for removing description element, please chime in.