This link is a small credit so that other people can also use our free theme. However, our theme is 100% GPL so you can edit and modify according to your requirements. There is a file called template-functions.php inside the inc folder which is having this footer function.
Yes, you can remove it. Please follow the steps below
1) Go to theme root folder ie (wp-content/themes/crater-free/)
2) Go to inc folder and find file template-functions.php and open this file with any text editor
3) Find line number 15 and remove the <span></span> tag completely
4) Save the file