Remove unused authentication_token column

This column dates back to 2013, when token authentication was removed
from Devise. We should not keep it.

This allows new stores to start without the unused column, while old
stores can still use any tokens they might be using.

Author: mamhoff

db/migrate/20101026184950_rename_columns_for_devise.rb

@@ -14,14 +14,12 @@ def up
     rename_column :spree_users, :last_login_at, :last_sign_in_at
     rename_column :spree_users, :current_login_ip, :current_sign_in_ip
     rename_column :spree_users, :last_login_ip, :last_sign_in_ip
-    add_column :spree_users, :authentication_token, :string
     add_column :spree_users, :unlock_token, :string
     add_column :spree_users, :locked_at, :datetime
     remove_column :spree_users, :openid_identifier
   end
 
   def down
-    remove_column :spree_users, :authentication_token
     remove_column :spree_users, :locked_at
     remove_column :spree_users, :unlock_token
     rename_column :spree_users, :last_sign_in_ip, :last_login_ip