Remove old BORINGSSL_YYYYMM defines.

They haven't been needed for a while now.

Change-Id: I4c24799f6692aa8fe8ea8f09795d4e7973baf7d7
Reviewed-on: https://boringssl-review.googlesource.com/19145
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>

include/openssl/base.h

@@ -136,8 +136,6 @@ extern "C" {
 #endif
 
 #define OPENSSL_IS_BORINGSSL
-#define BORINGSSL_201512
-#define BORINGSSL_201603
 #define OPENSSL_VERSION_NUMBER 0x100020af
 #define SSLEAY_VERSION_NUMBER OPENSSL_VERSION_NUMBER