Remove some easy obj.h dependencies.

A lot of consumers of obj.h only want the NID values. Others didn't need
it at all. This also removes some OBJ_nid2sn and OBJ_nid2ln calls in EVP
error paths which isn't worth pulling a large table in for.

BUG=chromium:499653

Change-Id: Id6dff578f993012e35b740a13b8e4f9c2edc0744
Reviewed-on: https://boringssl-review.googlesource.com/7563
Reviewed-by: David Benjamin <davidben@google.com>
diff --git a/include/openssl/x509.h b/include/openssl/x509.h
index 752191d..4b977b9 100644
--- a/include/openssl/x509.h
+++ b/include/openssl/x509.h
@@ -76,6 +76,7 @@
 #include <openssl/ecdsa.h>
 #include <openssl/ec.h>
 #include <openssl/evp.h>
+#include <openssl/obj.h>
 #include <openssl/rsa.h>
 #include <openssl/sha.h>
 #include <openssl/stack.h>