You need to write an ExpressionEngine Accessory. Accessories allow you to inject code into Control Panel pages.

https://ellislab.com/expressionengine/user-guide/development/accessories.html

Please go that route, and not the "let's edit core files derp derp" route. You can use this method to inject some jQuery using a function like this:

ee()->cp->add_to_foot('
<script>
    $(document).ready(function(){
        $('.class-of-unchanged-template-rows-goes-here').remove();
    });
</script>
');

This answer has a more thorough example of how an accessory is structured:

Include custom JavaScript in the control panel

You need to write an ExpressionEngine Accessory. Accessories allow you to inject code into Control Panel pages.

https://ellislab.com/expressionengine/user-guide/development/accessories.html

Please go that route, and not the "let's edit core files derp derp" route. You can use this method to inject some jQuery using a function like this:

ee()->cp->add_to_foot('
<script>
    $(document).ready(function(){
        $('.class-of-unchanged-template-rows-goes-here').remove();
    });
</script>
');

This answer has a more thorough example of how an accessory is structured:

Include custom JavaScript in the control panel