docs-xml: Fix usernames in pam_winbind manpages

docs-xml: Fix usernames in pam_winbind manpages

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14358

Signed-off-by: Andreas Schneider <asn@samba.org>
Reviewed-by: Alexander Bokovoy <ab@samba.org>
Autobuild-User(master): Andreas Schneider <asn@cryptomilk.org>
Autobuild-Date(master): Wed Apr 29 09:44:55 UTC 2020 on sn-devel-184

(cherry picked from commit 3abd92d7824e803f1ff53425088ebee30b58894b)

Autobuild-User(v4-11-test): Karolin Seeger <kseeger@samba.org>
Autobuild-Date(v4-11-test): Thu May 14 15:42:16 UTC 2020 on sn-devel-184