chore: remove unnecessary pam header uses

those actually cause issues when trying to cross-compile

src/auth.c

@@ -1,8 +1,6 @@
 #include <errno.h>
 #include <grp.h>
 #include <pwd.h>
-#include <security/_pam_types.h>
-#include <security/pam_appl.h>
 #include <security/pam_misc.h>
 #include <stdio.h>
 #include <stdlib.h>