We don't use whenever anymore. Lets remove the schedule file

**Why is this needed?**

Not really needed, but having code that is not used around is confusing, so lets
remove it

Signed-off-by: Jeroen van Baarsen <jeroenvanbaarsen@gmail.com>

config/schedule.rb

-# Use this file to easily define all of your cron jobs.
-#
-# If you make changes to this file, please create also an issue on
-# https://gitlab.com/gitlab-org/omnibus-gitlab/issues . This is necessary
-# because the omnibus packages manage cron jobs using Chef instead of Whenever.
-every 1.hour do
-  rake "ci:schedule_builds"
-end