email/eve: use Rust function to hash buffer to hex

Use SCMd5HashBufferToHex to hash the subject to a hex string.
Removes snprintf loop.

src/output-json-email-common.c

@@ -131,15 +131,10 @@ static void EveEmailLogJSONMd5(OutputJsonEmailCtx *email_ctx, JsonBuilder *js, S
         }
         field = MimeDecFindField(entity, "subject");
         if (field != NULL) {
-            unsigned char md5[SC_MD5_LEN];
-            char smd5[256];
+            char smd5[SC_MD5_HEX_LEN + 1];
             char *value = BytesToString((uint8_t *)field->value , field->value_len);
             if (value) {
-                size_t i,x;
-                SCMd5HashBuffer((uint8_t *)value, strlen(value), md5, sizeof(md5));
-                for (i = 0, x = 0; x < sizeof(md5); x++) {
-                    i += snprintf(smd5 + i, 255 - i, "%02x", md5[x]);
-                }
+                SCMd5HashBufferToHex((uint8_t *)value, strlen(value), smd5, sizeof(smd5));
                 jb_set_string(js, "subject_md5", smd5);
                 SCFree(value);
             }