* gnu/home/services/ssh.scm (serialize-address-family): Use the public API of
the maybe infrastructure.
* gnu/services/file-sharing.scm (serialize-maybe-string): Use maybe-value.
(serialize-maybe-file-object): Use maybe-value-set?.
* gnu/services/getmail.scm (getmail-retriever-configuration): Don't use
internals in unset field declarations.
(getmail-destination-configuration): Ditto.
* gnu/services/messaging.scm (raw-content?): Use maybe-value-set?.
(prosody-configuration): Use %unset-value.
* gnu/services/telephony.scm (jami-shepherd-services): Use maybe-value-set?.
(archive-name->username): Use maybe-value-set?.
* tests/services/configuration.scm ("maybe type, no default"): Use
%unset-value.
Modified-by: Maxim Cournoyer <maxim.cournoyer@gmail.com>
Signed-off-by: Maxim Cournoyer <maxim.cournoyer@gmail.com>