gpgsm: Retire the new --ldapserver.

* sm/gpgsm.c (oKeyServer_deprecated): New.
(opts): Assign "ldapserver" to the new option and mark it as obsolete.

We want to use "ldapserver" in dirmngr but need to keep using
"keyserver" in gpgsm for existant versions of Kleopatra etc.

• GnuPG-bug-id: T5801