Merge branch 'fix-notes-refresh-relative-url' into 'master'

Fix live notes refresh in relative URL deployments

### What does this MR do?

This MR fixes URLs used for refreshing notes--the relative_url prefix was appended twice

### Why was this MR needed?

In case of `relative_url` installation, opening a page which does refresh notes (i.e. merge request), the page generates lots of 404 errors in the browser console. It turns out that the relative_url is prepended to the link twice.

Supersedes !233

See merge request !1048

CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 
 v 7.14.0 (unreleased)
+  - Fix URL used for refreshing notes if relative_url is present (Bartłomiej Święcki)
   - Fix Error 500 when browsing projects with no HEAD (Stan Hu)
   - Fix full screen mode for snippet comments (Daniel Gerhardt)
   - Fix 404 error in files view after deleting the last file in a repository (Stan Hu)

app/assets/javascripts/notes.js.coffee

@@ -10,7 +10,6 @@ class @Notes
 
   constructor: (notes_url, note_ids, last_fetched_at, view) ->
     @notes_url = notes_url
-    @notes_url = gon.relative_url_root + @notes_url if gon.relative_url_root?
     @note_ids = note_ids
     @last_fetched_at = last_fetched_at
     @view = view