message: [Improvement] ImagePreview: remove unused code
diff: v-show="value"
  :class="b()"
  @touchstart="onTouchStart"
  - @touchmove.prevent="touchMove"
  @touchend="onTouchEnd"
  @touchcancel="onTouchEnd"
  >
  @@ -20,12 +19,11 @@ import create from '../utils/create';
  import Popup from '../mixins/popup';
  import Swipe from '../swipe';
  import SwipeItem from '../swipe-item';
  -import Touch from '../mixins/touch';
  export default create({
  name: 'image-preview',
  - mixins: [Popup, Touch],
  + mixins: [Popup],
  components: {
  Swipe,
  @@ -51,9 +49,8 @@ export default create({
  },
  methods: {
  - onTouchStart(event) {
  + onTouchStart() {
  this.touchStartTime = new Date();
  - this.touchStart(event);
  },
  onTouchEnd(event) {
  