Remove unneeded followers column from remoteusers

To migrate:

  ALTER TABLE `remoteusers` DROP `followers`;

schema.sql

@@ -156,7 +156,6 @@ CREATE TABLE IF NOT EXISTS `remoteusers` (
   `actor_id` varchar(255) NOT NULL,
   `inbox` varchar(255) NOT NULL,
   `shared_inbox` varchar(255) NOT NULL,
-  `followers` varchar(255) NOT NULL,
   PRIMARY KEY (`id`),
   UNIQUE KEY `collection_id` (`actor_id`)
 ) ENGINE=InnoDB DEFAULT CHARSET=latin1;