Breaks/Replaces bash-completion < 2.8

This was included in 2.8 release:

commit d962f3a3be2b5c3811e546890c99b19694c2a08e
Author: Ville Skyttä <ville.skytta@iki.fi>
Date:   Mon Sep 25 19:23:04 2017 +0300

    rfkill: Rename to _rfkill to avoid conflict with util-linux >= 2.31

This is needed for upgrades from stable/stretch which has
bash-completion 1:2.1-4.3. Can thus be dropped again once
buster is released (as far as Debian is concerned).

Closes: #913412

debian/control

@@ -377,6 +377,8 @@ Section: utils
 Priority: optional
 Pre-Depends: ${misc:Pre-Depends}
 Depends: ${misc:Depends}, ${shlibs:Depends}
+Breaks: bash-completion (<< 1:2.8~)
+Replaces: bash-completion (<< 1:2.8~)
 Multi-Arch: foreign
 Description: tool for enabling and disabling wireless devices
  rfkill is a simple tool for accessing the Linux rfkill device interface,