Remove the setup task from the maintenance docs

doc/raketasks/maintenance.md

-### Setup production application
-
-Runs the following rake tasks:
-
-* db:setup (Create the database, load the schema, and initialize with the seed data)
-* db:seed_fu (Loads seed data for the current environment.)
-* gitlab:app:enable_automerge (see "Features")
-
-```
-bundle exec rake gitlab:app:setup RAILS_ENV=production
-```
-
-
 ### Gather information about GitLab and the system it runs on
 This command gathers information about your GitLab installation and the System