Remove P-521 from the default supported curves list.

Per review comment on https://boringssl-review.googlesource.com/#/c/2843/.

Change-Id: I84c9320ff908c9f8912e83c6ece89d9b06c32bbf
Reviewed-on: https://boringssl-review.googlesource.com/2860
Reviewed-by: Adam Langley <agl@google.com>

ssl/t1_lib.c

diff --git a/ssl/t1_lib.c b/ssl/t1_lib.c
index 339c765..d2d2bc3 100644
--- a/ssl/t1_lib.c
+++ b/ssl/t1_lib.c
@@ -369,7 +369,6 @@
 static const uint16_t eccurves_default[] = {
     23, /* X9_64_prime256v1 */
     24, /* secp384r1 */
-    25, /* secp521r1 */
 };
 
 int tls1_ec_curve_id2nid(uint16_t curve_id) {