Remove bootstrap media query from pagination scss

Based on: status-page#11

Currently inside src/components/base/pagination/pagination.scss there is a left over bootstrap media query:

@include media-breakpoint-down(xs) {
  .gl-pagination:not(.custom-rendering) {
    .prev-page-item,
    .next-page-item {
      span {
        display: none;
      }
    }
  }
}

Leaving this in breaks the way we import @gitlab/ui into projects and so we should aim to remove it so that the pagination component is not dependent on a custom media query.