Remove residual xpt_release_device() call left after r272406 cleanup.

Excessive release here could trigger use-after-free condition and kernel
panic on LUN 0 disconnect.

MFC after:	1 week


git-svn-id: svn+ssh://svn.freebsd.org/base/head@274756 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f