mkfs-util: Drop batch (b) and n flags from mcopy

The batch flag is bugged on older versions of mcopy causing failures
such as:

```
Internal error, size too big
Streamcache allocation problem:: 5
```

It's also a little unclear what the batch flag actually does, so since
everything still works without it, it doesn't hurt to remove it.

The n flag only applies when copying from fat to unix which we don't do
so it doesn't make sense in this scenario.

src/shared/mkfs-util.c

@@ -148,7 +148,7 @@ static int do_mcopy(const char *node, const char *root) {
         if (r < 0)
                 return log_error_errno(r, "Failed to determine whether mcopy binary exists: %m");
 
-        argv = strv_new(mcopy, "-b", "-s", "-p", "-Q", "-n", "-m", "-i", node);
+        argv = strv_new(mcopy, "-s", "-p", "-Q", "-m", "-i", node);
         if (!argv)
                 return log_oom();