Revert "Fix incorrect expected error in ztest"

[behlendorf]

Motivation and Context

Revisiting #15295. A recent example of this failure in the CI can be found here:

https://github.com/openzfs/zfs/actions/runs/16007042925/attempts/3?pr=17501

Description

This reverts commit 2076011. The comment which explains EINVAL should be expected for this case was wrong, not the code. The kernel will return ENOTSUP when attaching a distributed spare to the wrong top-level dRAID vdev. See the check for this in spa_vdev_attach().

        /*
         * A dRAID spare can only replace a child of its parent dRAID vdev.
         */
        if (newvd->vdev_ops == &vdev_draid_spare_ops &&
            oldvd->vdev_top != vdev_draid_spare_get_parent(newvd)) {
                return (spa_vdev_exit(spa, newrootvd, txg, ENOTSUP));
        }

How Has This Been Tested?

Locally tested. During that testing I noticed a slightly different case which may explain the confusion here. During one run somehow ztest ended up adding a distributed spare for a top-level dRAID device which doesn't exist. In this case, EINVAL was returned instead ENOTSUP, however it should be impossible to manipulate a pool in to this layout. I wasn't able to manually reproduce the issue, so more debugging will be needed. That can be handled in a different PR.

Simplified example invalid pool config observed by ztest. Attaching draid1-1-0 will correctly return EINVAL, the draid1-1-0 distributed spare should not exist.

  pool: tank
 state: ONLINE
config:

	NAME                 STATE     READ WRITE CKSUM
	tank                 ONLINE       0     0     0
	  draid1:1d:3c:1s-0  ONLINE       0     0     0
	    /tmp/vdev1       ONLINE       0     0     0
	    /tmp/vdev2       ONLINE       0     0     0
	    /tmp/vdev3       ONLINE       0     0     0
	  draid1:1d:4c:2s-2  ONLINE       0     0     0
	    /tmp/vdev5       ONLINE       0     0     0
	    /tmp/vdev6       ONLINE       0     0     0
	    /tmp/vdev7       ONLINE       0     0     0
	    /tmp/vdev8       ONLINE       0     0     0
	spares
	  draid1-0-0         AVAIL   
	  draid1-2-0         AVAIL   
	  draid1-1-0         AVAIL   
	  draid1-2-1         AVAIL  

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Quality assurance (non-breaking change which makes the code more robust against bugs)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.