Remove VS 2015 support.

VS 2017 was released in March 2017, five years ago now. This means VS
2015 is now past our support window.

This will make the unmarked and "vs2017" configs in CI/CQ do the same
thing. I'll follow up with a separate CL in infra/config to switch the
test VS 2019 instead.

Update-Note: BoringSSL may no longer build with VS 2015. Consumers
should upgrade to the latest Visual Studio release. VS 2017 or later is
required.

Change-Id: I477759deb95a27efe132de76d9ed103826110df0
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/52085
Reviewed-by: Bob Beck <bbe@google.com>
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/ssl/ssl_key_share.cc b/ssl/ssl_key_share.cc
index c847a0a..920f25e 100644
--- a/ssl/ssl_key_share.cc
+++ b/ssl/ssl_key_share.cc
@@ -290,7 +290,7 @@
   HRSS_private_key hrss_private_key_;
 };
 
-CONSTEXPR_ARRAY NamedGroup kNamedGroups[] = {
+constexpr NamedGroup kNamedGroups[] = {
     {NID_secp224r1, SSL_CURVE_SECP224R1, "P-224", "secp224r1"},
     {NID_X9_62_prime256v1, SSL_CURVE_SECP256R1, "P-256", "prime256v1"},
     {NID_secp384r1, SSL_CURVE_SECP384R1, "P-384", "secp384r1"},