Remove unused services from the database

This adds a migration to remove unused services, where the properties
are empty. As the properties are empty, those do not contain any
settings or other information.

Fixes #25727

changelogs/unreleased/zj-remove-unused-services.yml

+---
+title: Remove unused and void services from the database
+merge_request:
+author:

db/post_migrate/20161221140236_remove_unneeded_services.rb

+class RemoveUnneededServices < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  def up
+    execute("DELETE FROM services WHERE active = false AND properties = '{}';")
+  end
+
+  def down
+    # noop
+  end
+end

db/schema.rb

@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20161220141214) do
+ActiveRecord::Schema.define(version: 20161221140236) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"