hook_uninstall()Remove any information that the module sets.
The information that the module should remove includes:
The module should not remove its entry from the {system} table. Database tables defined by hook_schema() will be removed automatically.
The uninstall hook will fire when the module gets uninstalled but before the module's database tables are removed, allowing your module to query its own tables during this routine.
@see hook_schema()
modules/system/system.api.php, line 2325
<?php
function hook_uninstall() {
variable_del('upload_file_types');
}
?>