global: Adapt to new var_expand API

src/lib-sieve/plugins/vacation/cmd-vacation.c

src/lib-sieve/storage/ldap/sieve-ldap-db.c

src/managesieve/managesieve-client.c

src/managesieve/managesieve-settings.c

src/plugins/lda-sieve/lda-sieve-plugin.c

tests/extensions/vacation/message.svtest