Remove WebSub subscriptions (#11303)

db/post_migrate/20190715031050_drop_subscriptions.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+class DropSubscriptions < ActiveRecord::Migration[5.2]
+  def up
+    drop_table :subscriptions
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end