Disable timeout while removing services

On GitLab.com this migration could take about 3 minutes. Disabling the
statement we know we have enough time to complete this.

Fixes #25976

db/post_migrate/20161221140236_remove_unneeded_services.rb

@@ -4,6 +4,8 @@ class RemoveUnneededServices < ActiveRecord::Migration
   DOWNTIME = false
   def up
+    disable_statement_timeout
+
     execute("DELETE FROM services WHERE active = false AND properties = '{}';")
   end