I can't remove #theme_wrappers functions from $variables in hook_preprocess_HOOK

Hi! I want to remove fieldset wrapper around radios element in my custom form. For this I use hook_preprocess_HOOK:

function mymodule_preprocess_radios(&$variables) {
  $variables['element']['#theme_wrappers'] = [];
}

But fieldset wrapper all the same remains in output html on page.
How to remove fieldset tag ?

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