usermod: allow all group types with -G option

usermod: allow all group types with -G option

The only way of removing a group from the supplementary list is to use
-G option, and list all groups that the user is a member of except for
the one that wants to be removed. The problem lies when there's a user
that contains both local and remote groups, and the group to be removed
is a local one. As we need to include the remote group with -G option
the command will fail.

This reverts commit 140510de9de4771feb3af1d859c09604043a4c9b. This way,
it would be possible to remove the remote groups from the supplementary
list.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1967641
Resolves: https://github.com/shadow-maint/shadow/issues/338

Signed-off-by: Iker Pedrosa <ipedrosa@redhat.com>