Move locked_at removal to post-deployment migration

app/models/merge_request.rb

@@ -9,6 +9,7 @@ class MergeRequest < ActiveRecord::Base
   include CreatedAtFilterable
 
   ignore_column :position
+  ignore_column :locked_at
 
   include ::EE::MergeRequest
 

db/migrate/20170801000000_remove_locked_at_column_from_merge_requests.rb → db/post_migrate/20170807160457_remove_locked_at_column_from_merge_requests.rb

@@ -6,6 +6,6 @@ class RemoveLockedAtColumnFromMergeRequests < ActiveRecord::Migration
   end
 
   def down
-    add_column :merge_requests, :locked_at, :datetime_with_timezone
+    # nothing to do to recover the values
   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: 20170803130232) do
+ActiveRecord::Schema.define(version: 20170807160457) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"