When you will delete the front-page.php your site will not show the Slider, Testimonials, Clients. The site will show the Blog Pots or Page as per the configuration of WP-Admin > Settings > Reading
You can remove the front-page.php file getting access to your server/hosting via any FTP Client
But, you can still do the thing without deleting the front-page.php file. We recommend this.
You can Hide the Featured Posts, Show the Posts/Page as per the WordPress Reading Settings from WP-Admin > Appearance > Writing Board Options > General Options
You can hide the Slide Unchecking This. Similarly, you can hide the Testimonials, Clients etc. from the Respective Tabs.
For Showing Selected Posts in the Slider you should check these during Post Creating/Editing
Extended Version has this advanced feature because all posts may not be same important for showing in Front Page Slider or List.
We request you to go through all available options under WP-Admin > Appearance > Writing Board Options