Remove BN_MONT_CTX_init.

One less exported function. Nothing ever stack-allocates them, within BoringSSL
or in consumers. This avoids the slightly odd mechanism where BN_MONT_CTX_free
might or might not free the BN_MONT_CTX itself based on a flag.

(This is also consistent with OpenSSL 1.1.x which does away with the _init
variants of both this and BIGNUM so it shouldn't be a compatibility concern
long-term either.)

Change-Id: Id885ae35a26f75686cc68a8aa971e2ea6767ba88
Reviewed-on: https://boringssl-review.googlesource.com/6350
Reviewed-by: Adam Langley <alangley@gmail.com>

include/openssl/bn.h

diff --git a/include/openssl/bn.h b/include/openssl/bn.h
index 8de8cc4..46673dc 100644
--- a/include/openssl/bn.h
+++ b/include/openssl/bn.h
@@ -731,11 +731,7 @@
 /* BN_MONT_CTX_new returns a fresh BN_MONT_CTX or NULL on allocation failure. */
 OPENSSL_EXPORT BN_MONT_CTX *BN_MONT_CTX_new(void);
 
-/* BN_MONT_CTX_init initialises a stack allocated |BN_MONT_CTX|. */
-OPENSSL_EXPORT void BN_MONT_CTX_init(BN_MONT_CTX *mont);
-
-/* BN_MONT_CTX_free frees the contexts of |mont| and, if it was originally
- * allocated with |BN_MONT_CTX_new|, |mont| itself. */
+/* BN_MONT_CTX_free frees memory associated with |mont|. */
 OPENSSL_EXPORT void BN_MONT_CTX_free(BN_MONT_CTX *mont);
 
 /* BN_MONT_CTX_copy sets |to| equal to |from|. It returns |to| on success or
@@ -843,7 +839,6 @@
               * (Ni is only stored for bignum algorithm) */
   BN_ULONG n0[2]; /* least significant word(s) of Ni;
                      (type changed with 0.9.9, was "BN_ULONG n0;" before) */
-  int flags;
   int ri;    /* number of bits in R */
 };