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/handshake_server.cc b/ssl/handshake_server.cc
index 15820be..7678904 100644
--- a/ssl/handshake_server.cc
+++ b/ssl/handshake_server.cc
@@ -418,7 +418,7 @@
   // JDK 11 always sends extensions in a particular order.
   constexpr uint16_t kMaxFragmentLength = 0x0001;
   constexpr uint16_t kStatusRequestV2 = 0x0011;
-  static CONSTEXPR_ARRAY struct {
+  static constexpr struct {
     uint16_t id;
     bool required;
   } kJavaExtensions[] = {
diff --git a/ssl/internal.h b/ssl/internal.h
index 8f68fc5..0087e7f 100644
--- a/ssl/internal.h
+++ b/ssl/internal.h
@@ -245,14 +245,6 @@
   { abort(); }
 #endif
 
-// CONSTEXPR_ARRAY works around a VS 2015 bug where ranged for loops don't work
-// on constexpr arrays.
-#if defined(_MSC_VER) && !defined(__clang__) && _MSC_VER < 1910
-#define CONSTEXPR_ARRAY const
-#else
-#define CONSTEXPR_ARRAY constexpr
-#endif
-
 // Array<T> is an owning array of elements of |T|.
 template <typename T>
 class Array {
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"},