Remove a pointless "#if 0" block from BN_mul.

Reviewed-by: NAndy Polyakov <appro@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/3683)

crypto/bn/bn_mul.c

@@ -587,46 +587,6 @@ int BN_mul(BIGNUM *r, const BIGNUM *a, const BIGNUM *b, BN_CTX *ctx)
             rr->top = top;
             goto end;
         }
-# if 0
-        if (i == 1 && !BN_get_flags(b, BN_FLG_STATIC_DATA)) {
-            BIGNUM *tmp_bn = (BIGNUM *)b;
-            if (bn_wexpand(tmp_bn, al) == NULL)
-                goto err;
-            tmp_bn->d[bl] = 0;
-            bl++;
-            i--;
-        } else if (i == -1 && !BN_get_flags(a, BN_FLG_STATIC_DATA)) {
-            BIGNUM *tmp_bn = (BIGNUM *)a;
-            if (bn_wexpand(tmp_bn, bl) == NULL)
-                goto err;
-            tmp_bn->d[al] = 0;
-            al++;
-            i++;
-        }
-        if (i == 0) {
-            /* symmetric and > 4 */
-            /* 16 or larger */
-            j = BN_num_bits_word((BN_ULONG)al);
-            j = 1 << (j - 1);
-            k = j + j;
-            t = BN_CTX_get(ctx);
-            if (al == j) {      /* exact multiple */
-                if (bn_wexpand(t, k * 2) == NULL)
-                    goto err;
-                if (bn_wexpand(rr, k * 2) == NULL)
-                    goto err;
-                bn_mul_recursive(rr->d, a->d, b->d, al, t->d);
-            } else {
-                if (bn_wexpand(t, k * 4) == NULL)
-                    goto err;
-                if (bn_wexpand(rr, k * 4) == NULL)
-                    goto err;
-                bn_mul_part_recursive(rr->d, a->d, b->d, al - j, j, t->d);
-            }
-            rr->top = top;
-            goto end;
-        }
-# endif
     }
 #endif                          /* BN_RECURSION */
     if (bn_wexpand(rr, top) == NULL)