ftpd: stop using -g flag for /bin/ls

In 3bfbb521 the behaviour of ls was changed such that -g was no longer
a noop for compatibility with BSD 4.3, but instead changed the output
of long mode to exclude the owner of the file and display only the
group.

Update how FTPd invokes ls to restore the previous behaviour

Reported-by: Andrew Fengler <andrew.fengler@scaleengine.com>
Reviewed-by: jrtc27, des, imp
Approved by: re (cperciva)
MFC after: 3 days
Sponsored-by: ScaleEngine Inc.
Fixes: 3bfbb521fef5 ("ls: Improve POSIX compatibility for -g and -n.")

(cherry picked from commit 5af3225e0448be6af7f0312e10d2a1dfbe150c25)
(cherry picked from commit e5fadc41b48045d8978993d6c4ac72c64542b470)