As noted by greyelf in their answer, deleting a player's saves is generally not something you want to do without their consent. In your specific case, I suppose it works out.
Try something like the following: (EDIT: updated the code to work anywhere)
<<script>>
Dialog.addClickHandler(
jQuery('<a id="game-restart">Restart</a>').appendTo(output),
null,
function () {
jQuery(Dialog.setup(L10n.get('restartTitle'), 'restart'))
.append(
'<p>' + L10n.get('restartPrompt') + '</p><ul class="buttons">'
+ '<li><button id="restart-ok">' + L10n.get(['restartOk', 'ok']) + '</button></li>'
+ '<li><button id="restart-cancel" class="ui-close">' + L10n.get(['restartCancel', 'cancel']) + '</button></li>'
+ '</ul>'
)
.find('#restart-ok')
.ariaClick({ one : true }, function () {
jQuery(document).one(':dialogclose', function () {
Save.clear();
Engine.restart();
});
Dialog.close();
});
}
);
<</script>>