NSS: Do not use deprecated header files

In file included from src/util/cert/nss/cert.c:26:
/usr/include/nss3/key.h:9:9: note: #pragma message: key.h is deprecated. Please include keyhi.h instead.
 #pragma message("key.h is deprecated. Please include keyhi.h instead.")
         ^~~~~~~

Merges: https://pagure.io/SSSD/sssd/pull-request/3930

Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>

src/util/cert/nss/cert.c

@@ -23,7 +23,7 @@
 #include <nss.h>
 #include <cert.h>
 #include <base64.h>
-#include <key.h>
+#include <keyhi.h>
 #include <prerror.h>
 #include <ocsp.h>
 #include <talloc.h>