s3:passdb: Remove unused function secrets_fetch_trust_account_password()

Signed-off-by: Pavel Filipenský <pfilipensky@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>

Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Mon Aug  8 19:03:08 UTC 2022 on sn-devel-184
