Remove hmac.h include from ssl.h.

base.h pulls in all the forward declarations, so this isn't needed.  We
should also remove bio.h and buf.h, but cURL seems to depend on those.
Code search suggests this one is okay though.

  case:yes content:\bHMAC content:openssl/ssl.h -content:openssl/hmac.h

Change-Id: Id91686bd134649245855025940bc17f82823c734
Reviewed-on: https://boringssl-review.googlesource.com/20364
Commit-Queue: David Benjamin <davidben@google.com>
Commit-Queue: Adam Langley <agl@google.com>
Reviewed-by: Adam Langley <agl@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
diff --git a/include/openssl/ssl.h b/include/openssl/ssl.h
index e9eb236..440c431 100644
--- a/include/openssl/ssl.h
+++ b/include/openssl/ssl.h
@@ -146,7 +146,6 @@
 
 #include <openssl/bio.h>
 #include <openssl/buf.h>
-#include <openssl/hmac.h>
 #include <openssl/lhash.h>
 #include <openssl/pem.h>
 #include <openssl/span.h>
diff --git a/ssl/ssl_session.cc b/ssl/ssl_session.cc
index 26d0b7b..e885324 100644
--- a/ssl/ssl_session.cc
+++ b/ssl/ssl_session.cc
@@ -142,6 +142,7 @@
 #include <utility>
 
 #include <openssl/err.h>
+#include <openssl/hmac.h>
 #include <openssl/lhash.h>
 #include <openssl/mem.h>
 #include <openssl/rand.h>