EVP_CIPHER_CTX_cleanup cannot fail.

There is exactly one implementation and it doesn't fail. Plus a cleanup
function that can fail is very bad manners; the caller has no choice but to
leak at that point.

Change-Id: I5b524617ef37bc7d92273472fa742416ea7dfd43
Reviewed-on: https://boringssl-review.googlesource.com/3564
Reviewed-by: Adam Langley <agl@google.com>

crypto/cipher/internal.h

diff --git a/crypto/cipher/internal.h b/crypto/cipher/internal.h
index 2b8fb05..f28fd4c 100644
--- a/crypto/cipher/internal.h
+++ b/crypto/cipher/internal.h
@@ -97,7 +97,7 @@
   int (*cipher)(EVP_CIPHER_CTX *ctx, uint8_t *out, const uint8_t *in,
                 size_t inl);
 
-  int (*cleanup)(EVP_CIPHER_CTX *);
+  void (*cleanup)(EVP_CIPHER_CTX *);
 
   int (*ctrl)(EVP_CIPHER_CTX *, int type, int arg, void *ptr);
 };