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/crypto/cipher/e_rc2.c b/crypto/cipher/e_rc2.c
index 8ca7bba..67418d5 100644
--- a/crypto/cipher/e_rc2.c
+++ b/crypto/cipher/e_rc2.c
@@ -55,7 +55,7 @@
  * [including the GNU Public Licence.] */
 
 #include <openssl/cipher.h>
-#include <openssl/obj.h>
+#include <openssl/nid.h>
 
 #include "internal.h"