Use this code...
.overlay-mode .sprocket-grids-b-readon {
display: none;
}
Put that wherever you keep custom CSS in that template.
How to change "READ MORE" in roksprocket.
http://www.rockettheme.com/forum/joomla-extension-roksprocket/185667-how-do-i-change-the-read-more-text-in-roksprocket?start=0#915542
To translate roksprocket literals....
http://www.rockettheme.com/forum/joomla-template-metropolis/190188-read-more-load-more-button-not-translated?start=0#934844
Regards, Mark.