If you grab the latest version of attendance from github for your site (as long as you are using Moodle 3.2 or higher)

I've just added a css class to that row that would allow you to hide it completely on your site using some css like this:

.path-mod-attendance .takelist .setallstatusesrow {
    display: none;
}

try adding that to your site custom css or your site theme and it might do what you need.

Note: this will only work if you use the latest version of the code from the github repo - the plugins db versions have not yet been updated with this change.