Remove spurious libelf dependency.

Submitted by:	pluknet


git-svn-id: svn+ssh://svn.freebsd.org/base/head@273778 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
Fix a regression in pw usermod -G list

The user was perperly adding the to different groups from "list" but was not
removed from the other groups it could have belong to.
While here add a regression test about this bug

PR:		185666
Reported by:	sub.mesa@gmail.com
MFC after:	1 week


git-svn-id: svn+ssh://svn.freebsd.org/base/head@273779 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f