It's hacky, but this will work ...
Put this in the grid's Advanced Initialization script:
Part 1
config.dataBound = function(e) {
removeButtonClass(e);
}
Part 2
function removeButtonClass(e){
let gridId = e.sender.element[0].id;
let buttons = $("#" + gridId).find("a.k-button");
$(buttons).removeClass("k-button");
}
If you have multiple grids you want to apply this to, I suggest putting Part 2 in a custom JS file.