ssl: Remove key exporter bug workaround

It is no longer necessary to cast the randbytes to non-const when
exporting keys.
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index f4bca87..a7facb8 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -1427,9 +1427,8 @@
                                       master, keyblk,
                                       mac_key_len, keylen,
                                       iv_copy_len,
-                                      /* work around bug in exporter type */
-                                      (unsigned char *) randbytes + 32,
-                                      (unsigned char *) randbytes,
+                                      randbytes + 32,
+                                      randbytes,
                                       tls_prf_get_type( tls_prf ) );
     }
 #endif