Docs lint: broken reference to img/import_csv_button.png

From https://gitlab.com/gitlab-org/gitlab-ee/pipelines/44391469/failures

Error: One or more checks failed
  Running check internal_links…   error
Issues found!
  public/doc/user/project/issues/index.html:
    [ ERROR ] internal_links - broken reference to img/import_csv_button.png
Running after script...
$ date
Tue Jan 22 22:33:02 UTC 2019
ERROR: Job failed: exit code 1

It looks like this was removed in https://gitlab.com/gitlab-org/gitlab-ee/commit/d19f2c28f7797d8fb37aaebd4378d08d1296a2ad