rpki-client: replace deprecated ERR_remove_state

[Claudio Jeker]

ERR_remove_state(0) is deprecated use the new api
ERR_remove_thread_state(NULL) instead.

-- 
:wq Claudio

Index: main.c
===================================================================
RCS file: /cvs/src/usr.sbin/rpki-client/main.c,v
retrieving revision 1.61
diff -u -p -r1.61 main.c
--- main.c      1 Apr 2020 14:15:49 -0000       1.61
+++ main.c      16 Apr 2020 10:01:56 -0000
@@ -1250,7 +1250,7 @@ out:
 
        EVP_cleanup();
        CRYPTO_cleanup_all_ex_data();
-       ERR_remove_state(0);
+       ERR_remove_thread_state(NULL);
        ERR_free_strings();
 
        exit(rc);