Fix use-after-free introduced in r274843.

I've missed that iscsi_outstanding_remove() frees the second pointer,
so it should no longer be used.  And in fact we don't really need to.

MFC after:	2 weeks


git-svn-id: svn+ssh://svn.freebsd.org/base/head@274845 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f