The two k-... classes are added, because they are the default CSS classes of the built-in Grid command buttons.
Apart from modifying the CSS code to override the Kendo UI styles, you can remove the k-... classes in the Grid's dataBound event:
Note that this may lead to undesired side effects, e.g. changes in the buttons' layout or position. In this case, you will need to apply back some of the k-button styles to the btn-warning class.
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