Delete a user role from database.
$role: A string with the role ID.
function user_role_delete($role) {
$role = user_role_load($role);
db_delete('role')
->condition('rid', $role->rid)
->execute();
db_delete('role_permission')
->condition('rid', $role->rid)
->execute();
// Update the users who have this role set:
db_delete('users_roles')
->condition('rid', $role->rid)
->execute();
module_invoke_all('user_role_delete', $role);
// Clear the user access cache.
drupal_static_reset('user_access');
drupal_static_reset('user_role_permissions');
}