Convert reference counts in crypto/

This change converts the reference counts in crypto/ to use
|CRYPTO_refcount_t|. The reference counts in |X509_PKEY| and |X509_INFO|
were never actually used and so were dropped.

Change-Id: I75d572cdac1f8c1083c482e29c9519282d7fd16c
Reviewed-on: https://boringssl-review.googlesource.com/4772
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/include/openssl/dsa.h b/include/openssl/dsa.h
index 2271915..7274e4c 100644
--- a/include/openssl/dsa.h
+++ b/include/openssl/dsa.h
@@ -354,7 +354,7 @@
   /* Normally used to cache montgomery values */
   CRYPTO_MUTEX method_mont_p_lock;
   BN_MONT_CTX *method_mont_p;
-  int references;
+  CRYPTO_refcount_t references;
   CRYPTO_EX_DATA ex_data;
   DSA_METHOD *meth;
   /* functional reference if 'meth' is ENGINE-provided */