Actually, to remove fields too:
$group_key = 'group_foo';
$fields = acf_get_local_fields( $group_key );
foreach ( $fields as $field ) {
acf_remove_local_field( $field['key'] );
acf_get_local_store( 'fields' )->remove( $field['key'] );
}
acf_remove_local_field_group( $group_key );
acf_get_store( 'field-groups' )->remove( $group_key );