How to remove author name and date created from Simplenews emails?
I would suggest you two options:


You can put node.tpl.php specific to your simplenews content-type and remove the unnecessary content from it. 
Add css file specific to the mailing system. I use mimemail system, so I did the following:


function THEME_NAME_preprocess_mimemail_message(&amp;$variables) {
  drupal_add_css(drupal_get_path('theme', 'THEME_NAME').'/css/mail.css');
}

In the mail.css, you can hide those fields using display:none;