Unset dropbutton/splitbutton in Drupal 8.3.x (convert dropbutton to side-by-side buttons)

dropbutton-unset.scss

@media screen and (min-width: 640px) {
  .form-actions .dropbutton-wrapper {
    float: none;
  }
}

.js .form-actions .dropbutton-widget,
.js td .dropbutton-widget,
.dropbutton-widget {
  border: 0;
}

/* UL styles are over-scoped in core, so this selector needs weight parity. */
.dropbutton-widget .dropbutton,
.js .dropbutton-widget .dropbutton {
  border: 0;
}

.dropbutton li,
.js .dropbutton li {
  display: block;

  @media screen and (min-width: 640px) {
    display: inline-block;
  }
}

.dropbutton .dropbutton-action input {
  padding: 0.5em 1.5em;
  white-space: normal;
  width: 100%;

  @media screen and (min-width: 640px) {
    width: auto;
  }
}

.js .dropbutton-multiple .dropbutton-widget {
  padding-right: 0;
}

.dropbutton-multiple .dropbutton .secondary-action {
  display: block;
  border: 0;

  @media screen and (min-width: 640px) {
    display: inline-block;
  }
}

.dropbutton .dropbutton-toggle,
.js .dropbutton .dropbutton-toggle,
.dropbutton .dropbutton-arrow,
.js .dropbutton .dropbutton-arrow {
  display: none;
}

There is an open issue in Drupal core to remove dropbuttons from the node publish/save interface. In the meantime, this is one way to unset the dropbuttons with just a CSS override.