Add libuserdefs and use in cmd/{oamuser,passwd}

@@ -93,12 +93,10 @@
 extern int putusrdef(), valid_uid();
 extern int call_passmgmt(), edit_group(), create_home();
 extern int edit_project();
 extern int **valid_lgroup();
 extern projid_t **valid_lproject();
-extern void update_def(struct userdefs *);
-extern void import_def(struct userdefs *);
 extern int get_default_zfs_flags();
 
 static uid_t uid;                       /* new uid */
 static char *logname;                   /* login name to add */
 static struct userdefs *usrdefs;        /* defaults for useradd */