Revert "Merge branch 'sh-lock-version-not-null' into 'master'

This reverts commit ff39ccfc.

db/migrate/20160830232601_change_lock_version_not_null.rb

-class ChangeLockVersionNotNull < ActiveRecord::Migration
-  include Gitlab::Database::MigrationHelpers
-
-  DOWNTIME = false
-
-  def up
-    change_column_null :issues, :lock_version, true
-    change_column_null :merge_requests, :lock_version, true
-  end
-
-  def down
-  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: 20160830232601) do
+ActiveRecord::Schema.define(version: 20160827011312) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"