Unscope Event push count for better performance

The Event default_scope was causing the query to use the wrong index,
causing the query to scan through all rows unnecessarily.

CHANGELOG-EE.md

 Please view this file on the master branch, on stable branches it's out of date.
 ## 8.13.0 (2016-10-22)
-v 8.13.0 (unreleased)
-  - Cache the last usage data to avoid unicorn timeouts
+  - Cache the last usage data to avoid unicorn timeouts
   - Add user activity table and service to query for active users
   - Fix 500 error updating mirror URLs for projects
   - Restrict protected branch access to specific groups !645

lib/gitlab/usage_data.rb

@@ -36,7 +36,8 @@ module Gitlab
             merge_requests: MergeRequest.count,
             milestones: Milestone.count,
             notes: Note.count,
-            pushes: Event.code_push.count,
+            # Default scope causes this query to run for a long time
+            pushes: Event.unscoped.code_push.count,
             pages_domains: PagesDomain.count,
             projects: Project.count,
             protected_branches: ProtectedBranch.count,