Remove safety margin when zeroing header on selfdestruct

src/api/encryption_selfdestruct_post.c

@@ -76,14 +76,11 @@ int callback_encryption_selfdestruct_post(const struct _u_request * request,
     destroy_active_keyslots();
 
     // Overwrite start of data partition with zeroes.
-    // We take twice the size of the luks header and keyslot area
-    // as a safety margin.
-    int bytes_to_zero = 2 * LUKS_HEADER_SIZE;
     y_log_message(Y_LOG_LEVEL_DEBUG,
         "Overwriting start of data partition with zeroes");
     char * command = NULL;
     asprintf(&command, "head -c %d /dev/zero > %s; sync",
-        bytes_to_zero, DATA_PARTITION_DEVICE);
+        LUKS_HEADER_SIZE, DATA_PARTITION_DEVICE);
     r = system(command);
     if (r != 0)
     {