Removes sticky polyfill from the diff file headers

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/39145

app/assets/javascripts/diffs/components/diff_file_header.vue

@@ -2,7 +2,6 @@
 import { escape } from 'lodash';
 import { mapActions, mapGetters } from 'vuex';
 import { GlDeprecatedButton, GlTooltipDirective, GlLoadingIcon } from '@gitlab/ui';
-import { polyfillSticky } from '~/lib/utils/sticky';
 import ClipboardButton from '~/vue_shared/components/clipboard_button.vue';
 import Icon from '~/vue_shared/components/icon.vue';
 import FileIcon from '~/vue_shared/components/file_icon.vue';
@@ -124,9 +123,6 @@ export default {
       return s__('MRDiff|Show full file');
     },
   },
-  mounted() {
-    polyfillSticky(this.$refs.header);
-  },
   methods: {
     ...mapActions('diffs', [
       'toggleFileDiscussions',