HTML validation: submit button duplicate type attribute

[danchamp]

type="submit" in this button template is redundant and results in a duplicate type attribute, causing HTML validation errors:

localgov_theme/templates/form_element/input--submit.html.twig

Line 14 in f7b6b29

<button type="submit" {{ attributes.addClass(['btn', 'btn-primary', 'btn-sm', 'mt-2']) }}>

Example output from Croydon site directories:

<button type="submit"  data-drupal-selector="edit-submit-localgov-directory-channel-13" type="submit" id="edit-submit-localgov-directory-channel--13" value="Search" class="button js-form-submit form-submit btn btn-primary btn-sm mt-2">
  <span class="fa fa-chevron-right"></span>
  <span>Search</span>
</button>