nuageinit.7: Fix a couple of minor errors

Use the correct key name in the chpasswd section.
Remove a stray line to fix the description of 'password'.

Sponsored by: Chelsio Communications
Reviewed by: maxim
Differential Revision: https://reviews.freebsd.org/D55547

(cherry picked from commit df5014f71cff2c02f46afa8823370d7f61494bdb)