Fix IntColumnHandler::delete

So let's think on delete.

On MySQL / SQLite, not much needs to be done. When a dedicated table field gets dropped, the trigger is gone with it, no cleanup is necessary. When a shared table has two columns and one gets dropped then the trigger needs to be recreated but that's all, the same code can handle this. Changing the if (!$schema->fieldExists($table, $column_int)) { to

$int_exists = $schema->fieldExists($table, $column_int); 
if ($schema->fieldExists($table, $column) != $int_exists)) {
  $changed[] = $column_int; 
}
if (!$int_exists) {
  $schema->addField($table, $column_int, $spec);
}

is enough here. However, we need the test for the multiple column case before this can happen.

On PgSQL, table drop equally drops the trigger vs a column drop needs the relevant trigger dropped. The relevant function always needs to be dropped, though.

And this is not optional, if you drop a column in a shared table then the triggers will break the DB. However, that's insanely rare so I am not worried. This will be done in a few days.