cyrus-sasl: Drop unneeded group addition

The mail group is provided by base-passwd so would always be present. Therefore
drop the uneeded group addition from this recipe.

This works around the recent user cleanup code improvements which meant
this started causing failures for people.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Acked-by: Otavio Salvador <otavio@ossystems.com.br>
Tested-by: Otavio Salvador <otavio@ossystems.com.br>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Joe MacDonald <joe_macdonald@mentor.com>