wkd: Minor permission fix for created files.

* tools/wks-util.c (wks_cmd_install_key): Don't set u+x on the file.
(ensure_policy_file): No need to make the policy file group writable.

The policy file is rarely changed thus no need to g+w. Setting +x on
a plain file does not make sense at all.

• GnuPG-bug-id: T5214