Thereby fix apparmor issue.
> Dec 08 09:47:50 host audit[3232]: AVC apparmor="DENIED" operation="exec" profile="/usr/bin/whonixcheck" name="/usr/lib/security-misc/permission-lockdown" pid=3232 comm="sudo" requested_mask="x" denied_mask="x" fsuid=0 ouid=0
> Dec 08 09:47:50 host sudo[3232]: pam_exec(sudo:session): execve(/usr/lib/security-misc/permission-lockdown,...) failed: Permission denied
It is no longer required, because...
existing linux user accounts:
* Get permission lock down because security-misc `debian/security-misc.postinst` calls `/usr/lib/security-misc/permission-lockdown`.
new linux user accounts (created at first boot):
* security-misc `/usr/share/pam-configs/mkhomedir-security-misc` pam mkhomedir sets secure permissions using `umask=027`.