Remove ignore_column token from Operations::FeatureFlagsClient

Remove IgnorableColumns module

ee/app/models/operations/feature_flags_client.rb

@@ -3,10 +3,8 @@
 module Operations
   class FeatureFlagsClient < ApplicationRecord
     include TokenAuthenticatable
-    include IgnorableColumns
 
     self.table_name = 'operations_feature_flags_clients'
-    ignore_column :token, remove_after: '2019-12-15', remove_with: '12.6'
 
     belongs_to :project