Removing posted by admin date from a contact form
There are multiple ways you can do it


For all content of same content type


Go to the content type for which you want to hide Author info.
Scroll down to see the tabs at the bottom and select Display settings.
Uncheck Display author and date information.
Save content type

For Single Node


Go to node.tpl.php and search for $submitted
Give below condition for you case 

if ( arg(0) == 'node' AND is_numeric(arg(1)) AND arg(2) == FALSE AND arg(1)==7) {  print $submitted; }