Remove unnecessary id in anchor

- It seemed like we wanted this value to be
  bound to the id attribute, but it was
  actually literally the string "diffFile.file_path"
- This was over a year ago, so apprently this ID
  isn't actually needed for anything...

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

@@ -172,7 +172,6 @@ export default {
       />
       <a
         v-once
-        id="diffFile.file_path"
         ref="titleWrapper"
         class="append-right-4"
         :href="titleLink"