zed: mark disks as REMOVED when they are removed

[ixhamza]

Motivation and Context

zed: mark disks as REMOVED when they are removed

Description

ZED does not take any action for disk removal events if there is no spare VDEV
available.Added zpool_vdev_remove_wanted() in libzfs and vdev_remove_wanted()
in vdev.c to remove the VDEV through ZED on removal event. This means that if
you are running zed and remove a disk, it will be properly marked as REMOVED.
Upstream PR: openzfs#13797 (Merged)

How Has This Been Tested?

By hotplugging vdevs through QEMU

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)
• 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.