Remove redundant code.
if_detach already did these steps. Also, now we didn't keep routes to link-local
addresses.

Obtained from:	Yandex LLC
Sponsored by:	Yandex LLC


git-svn-id: svn+ssh://svn.freebsd.org/base/head@273858 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f