Do not use gpg --trust-model=always

- gpg will not create a trustdb when running with --update-trustdb with
   --trust-model=always:
       gpg: no need for a trustdb update with 'always' trust model
 - subsequent gpg calls will fail because there is no trustdb in GPGHOME

mmdebstrap

@@ -4986,7 +4986,6 @@ sub main() {
                     '--ignore-time-conflict', '--no-options',
                     '--no-default-keyring',   '--homedir',
                     $gpghome,                 '--no-auto-check-trustdb',
-                    '--trust-model',          'always'
                 );
                 my ($ret, $message);
                 {