CECPQ1: change from named curve to ciphersuite.

This is easier to deploy, and more obvious.  This commit reverts a few
pieces of e25775bc, but keeps most of it.

Change-Id: If8d657a4221c665349c06041bb12fffca1527a2c
Reviewed-on: https://boringssl-review.googlesource.com/8061
Reviewed-by: Adam Langley <agl@google.com>

ssl/ssl_lib.c

diff --git a/ssl/ssl_lib.c b/ssl/ssl_lib.c
index a27d430..3b8cff7 100644
--- a/ssl/ssl_lib.c
+++ b/ssl/ssl_lib.c
@@ -1725,6 +1725,9 @@
     mask_k |= SSL_kECDHE;
   }
 
+  /* CECPQ1 ciphers are always acceptable if supported by both sides. */
+  mask_k |= SSL_kCECPQ1;
+
   /* PSK requires a server callback. */
   if (ssl->psk_server_callback != NULL) {
     mask_k |= SSL_kPSK;