Remove RSA bignum_data that is not used anywhere

Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/14624)

crypto/rsa/rsa_lib.c

@@ -172,7 +172,6 @@ void RSA_free(RSA *r)
 #endif
     BN_BLINDING_free(r->blinding);
     BN_BLINDING_free(r->mt_blinding);
-    OPENSSL_free(r->bignum_data);
     OPENSSL_free(r);
 }
 

crypto/rsa/rsa_local.h

@@ -94,11 +94,6 @@ struct rsa_st {
     BN_MONT_CTX *_method_mod_n;
     BN_MONT_CTX *_method_mod_p;
     BN_MONT_CTX *_method_mod_q;
-    /*
-     * all BIGNUM values are actually in the following data, if it is not
-     * NULL
-     */
-    char *bignum_data;
     BN_BLINDING *blinding;
     BN_BLINDING *mt_blinding;
     CRYPTO_RWLOCK *lock;