Partially revert ebcd5711 to fix runner pages

What does this MR do?

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

The Admin runner page and runner details pages are broken right now. This change seems to have been introduced in ebcd5711 . The proper fix (possibly . !18738 (closed)) is probably a much longer process and so the safe option is to just revert for now.

To reproduce the problem simply add any runner then start that runner and go to Admin > Runners and you will see a 500.

The error is:

 ActionView::Template::Error:
       Object must be a Date, DateTime or Time object. "2018-05-04T07:29:50.365+02:00" given.
     # ./app/helpers/application_helper.rb:107:in `time_ago_with_tooltip'
     # ./app/views/admin/runners/_runner.html.haml:34:in `_app_views_admin_runners__runner_html_haml___349973184012124948_70097738702620'
     # ./app/views/admin/runners/index.html.haml:71:in `block in _app_views_admin_runners_index_html_haml__3432066315448256266_70097737665360'
     # ./app/views/admin/runners/index.html.haml:70:in `_app_views_admin_runners_index_html_haml__3432066315448256266_70097737665360'

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

/cc @tnir